William Herschel. (continued 2)

It was at this time, 1783, May 8, that Herschel married. His wife was the daughter of Mr. James Baldwin, a merchant of the city of London, and the widow of John Pitt, Esq. She is described as a lady of singular amiability and gentleness of character. She was entirely interested in his scientific pursuits, and the jointure which she brought removed all further anxiety about money affairs. They had but one child, John Frederick William, born March 7, 1792.[21]

The house at Datchet became more and more unfit for the needs of the family, and in June, 1785, a move was made to Clay Hall, in Old Windsor. The residence here was but short, and finally a last change was made to Slough on April, 3d, 1786.

The ardor of the work during these years can be judged of by a single sentence from Carolina Herschel's diary:

"The last night at Clay Hall was spent in sweeping till daylight, and by the next evening the telescope stood ready for observation at Slough."

From 1786 until his death, Herschel remained at Slough; his life, truly speaking, was in his observatory.

It is indeed true, as Arago has said in his eloquent tribute to him: "On peut dire hardiment du jardin et de la petite maison de Slough, que c'est le lieu du monde où il a été fait le plus de découvertes. Le nom de ce village ne périra pas; les sciences le transmettront religieusement à nos derniers neveux."

Herschel's first contribution to the Philosophical Transactions was printed in the volume for 1780, his last in that for 1818. Of these thirty-nine volumes, there are only two (1813 and 1817) which contain no paper from his hand, and many volumes contain more than one, as he published no less than sixty-eight memoirs in this place.

And yet it must not be thought that his was an austere and grave existence. Music, which he loved to enthusiasm, was still a delight to him. All the more that his devotion was free. The glimpses which we get of his life with his friends show him always cheerful, ardent, and devoted. Even in his later years, he had not lost a "boyish earnestness to explain;" his simplicity and the charm of his manner struck every one.

"Herschel, you know, and everybody knows, is one of the most pleasing and well-bred natural characters of the present age," says Dr. Burney, who had opportunity to know.

The portrait which is given in the frontispiece must have been painted about this time (1788), and the eager, ardent face shows his inner life far better than any words can do.

Even in his scientific writings, which everything conspired to render grave and sober, the almost poetic nature of his mind shows forth. In one of his (unpublished) note-books, now in the Royal Society's library, I found this entry:

"640th Sweep—November 28, 1786.—The nebula of Orion, which I saw by the front view, was so glaring and beautiful that I could not think of taking any place of its extent."

He was quite alone under the perfectly silent sky when this was written, and he was at his post simply to make this and other such observations. But the sky was beautiful to him, and his faithful sister, Carolina, sitting below, has preserved for us the words as they dropped from his lips.

On the 11th of January, 1787, Herschel discovered two satellites to Uranus.

After he had well assured himself of their existence, but before he communicated his discovery to the world, he made this crucial test. He prepared a sketch of Uranus attended by his two satellites, as it would appear on the night of February 10, 1787, and when the night came, "the heavens displayed the original of my drawings, by showing in the situation I had delineated them the Georgian planet attended by two satellites. I confess that this scene appeared to me with additional beauty, as the little secondary planets seemed to give a dignity to the primary one which raises it into a more conspicuous situation among the great bodies of the solar system.". . .

In a memoir of 1789, he has a few sentences which show the living way in which the heavens appeared to him:

"This method of viewing the heavens seems to throw them into a new kind of light. "They are now seen to resemble a luxuriant garden, which contains the greatest variety of productions in different flourishing beds; and one advantage we may at least reap from it is, that we can, as it were, extend the range of our experience to an immense duration. For is it not almost the same thing whether we live successively to witness the germination, blooming, foliage, fecundity, fading, withering, and corruption of a plant, or whether a vast number of specimens selected from every stage through which the plant passes in the course of its existence be brought at once to our view?"

The thought here is no less finely expressed than it is profound. The simile is perfect, if we have the power to separate among the vast variety each state of being from every other, and if the very luxuriance of illustration in the heavens does not bewilder and overpower the mind. It was precisely this discriminating power that Herschel possessed in perfection.

There is a kind of humor in the way he records a change of opinion:

"I formerly supposed the surface of Saturn's ring to be rough, owing to luminous points like mountains seen on it, till one of these was kind enough to venture off the edge of the ring and appear as a satellite."

In 1782 he replies with a certain concealed sharpness to the idea that he used magnifying powers which were too high. There is a tone almost of impatience, as if he were conscious he was replying to a criticism based on ignorance:

"We are told that we gain nothing by magnifying too much. I grant it; but shall never believe I magnify too much till by experience I find that I can see better with a lower power." (1782.)

By 1786, when he returns to this subject, in answer to a formal request to explain his use of high magnifiers, he is quite over any irritation, and treats the subject almost with playfulness:

"Soon after my first essay of using high powers with the Newtonian telescope, I began to doubt whether an opinion which has been entertained by several eminent authors, 'that vision will grow indistinct when the optic pencils are less than the fiftieth part of an inch,' would hold good in all cases. I perceived that according to this criterion I was not entitled to see distinctly with a power of much more than about 320 in a seven-foot telescope of an aperture of six and four-tenths inches, whereas in many experiments I found myself very well pleased with magnifiers which far exceeded such narrow limits. This induced me, as it were, by way of apology to myself for seeing well where I ought to have seen less distinctly, to make a few experiments."

It is needless to say that these experiments proved that from the point of view taken by Herschel, he was quite right, and that his high powers had numerous valuable applications. He goes on to say:

"Had it not been for a late conversation with some of my highly esteemed and learned friends, I might probably have left the papers on which these experiments were recorded, among the rest of those that are laid aside, when they have afforded me the information I want."

The last sentence seems to be a kind of notice to his learned friends that there is yet more unsaid. As a warning to those to whose criticisms he had replied, he gives them this picture of the kind of assiduity which will be required, if some of his observations on double stars are to be repeated:

"It is in vain to look for these stars if every circumstance is not favorable. The observer as well as the instrument must have been long enough out in the open air to acquire the same temperature. In very cold weather an hour at least will be required." (1782.)

We may gain some further insight into his character from the following chance extracts from his writings:

"I have all along had truth and reality in view as the sole object of my endeavors." (1782.)

"Not being satisfied when I thought it possible to obtain more accurate measures, I employed [a more delicate apparatus]." (1783.)

"To this end I have already begun a series of observations upon several zones of double stars, and should the result of them be against these conjectures, I shall be the first to point out their fallacy." (1783.)

"There is a great probability of succeeding still farther in this laborious but delightful research, so as to be able at last to say not only how much the annual parallax is not, but how much it really is." (1782.)

The nature of his philosophizing, and the limits which he set to himself, may be more clearly seen in further extracts:

"By taking more time [before printing these observations] I should undoubtedly be enabled to speak more confidently of the interior construction of the heavens, and of its various nebulous and sidereal strata. As an apology for this prematurity it may be said that, the end of all discoveries being communication, we can never be too ready in giving facts and observations, whatever we may be in reasoning upon them." (1785.)

"In an investigation of this delicate nature we ought to avoid two opposite extremes. If we indulge a fanciful imagination, and build worlds of our own, we must not wonder at our going wide from the path of truth and nature. On the other hand, if we add observation to observation without attempting to draw not only certain conclusions but also conjectural views from them, we offend against the very end for which only observations ought to be made. I will endeavor to keep a proper medium, but if I should deviate from that, I could wish not to fall into the latter error." (1785.)

"As observations carefully made should always take the lead of theories, I shall not be concerned if what I have to say contradicts what has been said in my last paper on this subject." (1790.)

No course of reasoning could be more simple, more exact, more profound, and more beautiful than this which follows:

"As it has been shown that the spherical figure of a cluster is owing to the action of central powers, it follows that those clusters which, cæteris paribus, are the most complete in this figure, must have been the longest exposed to the action of these causes. Thus the maturity of a sidereal system may be judged from the disposition of the component parts.

"Hence planetary nebulæ may be looked on as very aged. Though we cannot see any individual nebula pass through all its stages of life, we can select particular ones in each peculiar stage." (1789.)

There is something almost grandiose and majestic in his statement of the ultimate destiny of the Galaxy:

"To him the fates were known Of orbs dim hovering on the skirts of space."

"—Since the stars of the Milky Way are permanently exposed to the action of a power whereby they are irresistibly drawn into groups, we may be certain that from mere clustering stars they will be gradually compressed, through successive stages of accumulation, till they come up to what may be called the ripening period of the globular form, and total insulation; from which it is evident that the Milky Way must be finally broken up and cease to be a stratum of scattered stars.

"The state into which the incessant action of the clustering power has brought it at present, is a kind of chronometer that may be used to measure the time of its past and future existence; and although we do not know the rate of going of this mysterious chronometer, it is nevertheless certain that since the breaking up of the Milky Way affords a proof that it cannot last forever, it equally bears witness that its past duration cannot be admitted to be infinite." (1814.)

Herschel's relations with his cotemporaries were usually of the most pleasant character, though seldom intimate. This peace was broken but by one unpleasant occurrence. In the Philosophical Transactions for 1792, Schroeter had communicated a series of observations made with one of Herschel's own telescopes on the atmospheres of Venus, the Moon, etc. It was not only an account of phenomena which had been seen; it was accompanied by measures, and the computations based on these led to heights and dimensions for mountains on Venus which were, to say the least, extravagant. The adjective will not seem too strong when we say that the very existence of the mountains themselves is to-day more than doubtful.

The appearances seen by Schroeter were described by him in perfectly good faith, and similar ones have been since recorded. His reasoning upon them was defective, and the measures which he made were practically valueless. This paper, printed in the Transactions of the Royal Society, to which Schroeter had not before contributed, appears to have irritated Herschel.

No doubt there were not wanting members of his own society who hinted that on the Continent, too, there were to be found great observers, and that here, at least, Herschel had been anticipated even in his own field. I have always thought that the memoir of Herschel which appeared in the next volume of the Transactions (1793), Observations on the Planet Venus, was a rejoinder intended far more for the detractors at home than for the astronomer abroad. The review is conceived in a severe spirit. The first idea seems to be to crush an opposition which he feels. The truth is established, but its establishment is hardly the first object.

It seems as if Herschel had almost allowed himself to be forced into a position of arrogance, which his whole life shows was entirely foreign to his nature. All through the review he does not once mention Schroeter's name. He says:

"A series of observations on Venus, begun by me in April, 1777, has been continued down to the present time. . . . The result of my observations would have been communicated long ago if I had not flattered myself with the hope of some better success concerning the diurnal motion of Venus, which has still eluded my constant attention as far as concerns its period and direction. . . . Even at this present time I should hesitate to give the following extracts if it did not seem incumbent on me to examine by what accident I came to overlook mountains in this planet of such enormous height as to exceed four, five, or even six times the perpendicular height of Chimboraço, the highest of our mountains. . . . The same paper contains other particulars concerning Venus and Saturn. All of which being things of which I have never taken any notice, it will not be amiss to show, by what follows, that neither want of attention, nor a deficiency of instruments, would occasion my not perceiving these mountains of more than twenty-three miles in height, this jagged border of Venus, and these flat, spherical forms on Saturn."

The reply of Schroeter (1795) is temperate and just. It does him honor, and he generously gives full justice to his critic.

It would hardly be worth while to mention this slight incident if it were not that during these years there certainly existed a feeling that Herschel undervalued the labors of his cotemporaries.

This impression was fostered no doubt by his general habit of not quoting previous authorities in the fields which he was working.

A careful reading of his papers will, I think, show that his definite indebtedness to his cotemporaries was vanishingly small. The work of Michell and Wilson he alludes to again and again, and always with appreciation. Certainly he seems to show a vein of annoyance that the papers of Christian Mayer, De novis in cœlo sidereo phænomenis (1779), and Beobachtungen von Fixsterntrabanten (1778), should have been quoted to prove that the method proposed by Herschel in 1782 for ascertaining the parallax of the fixed stars by means of observations of those which were double, was not entirely original with himself.

There is direct proof that it was so,[22] and if this was not forthcoming it would be unnecessary, as he has amply shown in his Catalogue of Double Stars. One is reminded of his remarks on the use of the high magnifying powers by the impatience of his comments.

His proposal to call the newly discovered minor planets asteroids (1802) was received as a sign that he wished to discriminate between the discoveries of Piazzi and Olbers and his own discovery of Uranus.[23]

He takes pains to quietly put this on one side in one of his papers, showing that he was cognizant of the existence of such a feeling.

I am tempted to resurrect from a deserved obscurity a notice of Herschel's Observations on the Two Lately Discovered Celestial Bodies [23] (Philosophical Transactions, 1802), printed in the first volume of the Edinburgh Review, simply to show the kind of envy to which even he, the glory of England, was subject.

The reviewer sets forth the principal results of Herschel's observations, and, after quoting his definition of the new term asteroid, goes on to say:

"If a new name must be found, why not call them by some appellation which shall, in some degree, be descriptive of, or at least consistent with, their properties? Why not, for instance, call them Concentric Comets, or Planetary Comets, or Cometary Planets? or, if a single term must be found, why may we not coin such a phrase as Planetoid or Cometoid?"

Then follows a general arraignment of Herschel's methods of expression and thought, as distinguished from his powers of mere observation. This distinction, it may be said, exists only in the reviewer's mind; there was no such distinction in fact. If ever a series of observations was directed by profound and reasonable thought, it was Herschel's own.

"Dr. Herschel's passion for coining words and idioms has often struck us as a weakness wholly unworthy of him. The invention of a name is but a poor achievement for him who has discovered whole worlds. Why, for instance, do we hear him talking of the space-penetrating power of his instrument—a compound epithet and metaphor which he ought to have left to the poets, who, in some future age, shall acquire glory by celebrating his name. The other papers of Dr. Herschel, in the late volumes of the Transactions, do not deserve such particular attention. His catalogue of 500 new nebulæ, though extremely valuable to the practical astronomer, leads to no general conclusions of importance, and abounds with the defects which are peculiar to the Doctor's writings—a great prolixity and tediousness of narration—loose and often unphilosophical reflections, which give no very favorable idea of his scientific powers, however great his merit may be as an observer—above all, that idle fondness for inventing names without any manner of occasion, to which we have already alluded, and a use of novel and affected idioms.

* * * * * * *

"To the speculations of the Doctor on the nature of the Sun, we have many similar objections; but they are all eclipsed by the grand absurdity which he has there committed, in his hasty and erroneous theory concerning the influence of the solar spots on the price of grain. Since the publication of Gulliver's voyage to Laputa, nothing so ridiculous has ever been offered to the world. We heartily wish the Doctor had suppressed it; or, if determined to publish it, that he had detailed it in language less confident and flippant."

One is almost ashamed to give space and currency to a forgotten attack, but it yields a kind of perspective; and it is instructive and perhaps useful to view Herschel's labors from all sides, even from wrong and envious ones.

The study of the original papers, together with a knowledge of the circumstances in which they were written, will abundantly show that Herschel's ideas sprung from a profound meditation of the nature of things in themselves. What the origin of trains of thought prosecuted for years may have been we cannot say, nor could he himself have expressed it. A new path in science was to be found out, and he found it. It was not in his closet, surrounded by authorities, but under the open sky, that he meditated the construction of the heavens. As he says, "My situation permitted me not to consult large libraries; nor, indeed, was it very material; for as I intended to view the heavens myself, Nature, that great volume, appeared to me to contain the best catalogue."

His remarkable memoirs on the invisible and other rays of the solar spectrum were received with doubt, and with open denial by many of the scientific bodies of Europe. The reviews and notices of his work in this direction were often quite beyond the bounds of a proper scientific criticism; but Herschel maintained a dignified silence. The discoveries were true, the proofs were open to all, and no response was needed from him. He may have been sorely tempted to reply, but I am apt to believe that the rumors that reached him from abroad and at home did not then affect him as they might have done earlier. He was at his grand climacteric, he had passed his sixty-third year, his temper was less hasty than it had been in his youth, and his nerves had not yet received the severe strain from whose effects he suffered during the last years of his life.

We have some glimpses of his personal life in the reminiscences of him in the Diary and Letters of Madame D'Arblay, who knew him well:

"1786.—In the evening Mr. Herschel came to tea. I had once seen that very extraordinary man at Mrs. de Luc's, but was happy to see him again, for he has not more fame to awaken curiosity than sense and modesty to gratify it. He is perfectly unassuming, yet openly happy, and happy in the success of those studies which would render a mind less excellently formed presumptuous and arrogant.

"The king has not a happier subject than this man, who owes it wholly to His Majesty that he is not wretched; for such was his eagerness to quit all other pursuits to follow astronomy solely, that he was in danger of ruin, when his talents and great and uncommon genius attracted the king's patronage. He has now not only his pension, which gives him the felicity of devoting all his time to his darling study, but he is indulged in license from the king to make a telescope according to his new ideas and discoveries, that is to have no cost spared in its construction, and is wholly to be paid for by His Majesty.

"This seems to have made him happier even than the pension, as it enables him to put in execution all his wonderful projects, from which his expectations of future discoveries are so sanguine as to make his present existence a state of almost perfect enjoyment. Mr. Locke himself would be quite charmed with him.

"He seems a man without a wish that has its object in the terrestrial globe. At night Mr. Herschel, by the king's command, came to exhibit to His Majesty and the royal family the new comet lately discovered by his sister, Miss Herschel; and while I was playing at piquet with Mrs. Schwellenburg, the Princess Augusta came into the room and asked her if she chose to go into the garden and look at it. She declined the offer, and the princess then made it to me. I was glad to accept it for all sorts of reasons. We found him at his telescope. The comet was very small, and had nothing grand or striking in its appearance; but it is the first lady's comet, and I was very desirous to see it. Mr. Herschel then showed me some of his new discovered universes, with all the good humor with which he would have taken the same trouble for a brother or a sister astronomer; there is no possibility of admiring his genius more than his gentleness."

"1786, December 30th.—This morning my dear father carried me to Dr. Herschel. That great and very extraordinary man received us almost with open arms. He is very fond of my father, who is one of the council of the Royal Society this year, as well as himself. . . . At this time of day there was nothing to see but his instruments; those, however, are curiosities sufficient. . . . I wished very much to have seen his sister, . . . but she had been up all night, and was then in bed."

"1787, September.—Dr. Herschel is a delightful man; so unassuming with his great knowledge, so willing to dispense it to the ignorant, and so cheerful and easy in his general manners, that, were he no genius, it would be impossible not to remark him as a pleasing and sensible man."

"1788, October 3d.—We returned to Windsor at noon, and Mrs. de Luc sent me a most pressing invitation to tea and to hear a little music. Two young ladies were to perform at her house in a little concert. Dr. Herschel was there, and accompanied them very sweetly on the violin; his new-married wife was with him, and his sister. His wife seems good-natured; she was rich, too! and astronomers are as able as other men to discern that gold can glitter as well as stars."

DR. BURNEY TO MADAME D'ARBLAY.

"Chelsea College, September 28, 1798.

"* * * * *

"I drove through Slough in order to ask at Dr. Herschel's door when my visit would be least inconvenient to him—that night or next morning. The good soul was at dinner, but came to the door himself, to press me to alight immediately and partake of his family repast; and this he did so heartily that I could not resist.

* * * * * * *

"I expected (not knowing that Herschel was married) only to have found Miss Herschel; but there was a very old lady, the mother, I believe, of Mrs. Herschel, who was at the head of the table herself, and a Scots lady (a Miss Wilson, daughter of Dr. Wilson, of Glasgow, an eminent astronomer), Miss Herschel, and a little boy. They rejoiced at the accident which had brought me there, and hoped I would send my carriage away and take a bed with them. They were sorry they had no stables for my horses.

"We soon grew acquainted—I mean the ladies and I—and before dinner was over we seemed old friends just met after a long absence. Mrs. Herschel is sensible, good-humored, unpretending, and well bred; Miss Herschel all shyness and virgin modesty; the Scots lady sensible and harmless; and the little boy entertaining, promising, and comical. Herschel, you know, and everybody knows, is one of the most pleasing and well-bred natural characters of the present age, as well as the greatest astronomer.

"Your health was drunk after dinner (put that into your pocket), and after much social conversation and a few hearty laughs, the ladies proposed to take a walk, in order, I believe, to leave Herschel and me together. We walked and talked round his great telescopes till it grew damp and dusk, then retreated into his study to philosophize.

* * * * * * *

"He made a discovery to me, which, had I known it sooner, would have overset me, and prevented my reading any part of my work.[24] He said that he had almost always had an aversion to poetry, which he regarded as the arrangement of fine words, without any useful meaning or adherence to truth; but that when truth and science were united to these fine words, he liked poetry very well."

1798, December 10.

DR. BURNEY TO MADAME D'ARBLAY.

"Herschel has been in town for short spurts, and back again two or three times, leaving Mrs. Herschel behind (in town) to transact law business. I had him here two whole days."

The reading of the manuscript of the Poetical History of Astronomy was continued, "and Herschel was so humble as to confess that I knew more of the history of astronomy than he did, and had surprised him with the mass of information I had got together.

"He thanked me for the entertainment and instruction I had given him. 'Can anything be grander?' and all this before he knows a word of what I have said of himself—all his discoveries, as you may remember, being kept back for the twelfth and last book."

DR. BURNEY TO MADAME D'ARBLAY.

"Slough, Monday morning. July 22, 1799, in bed at Dr. Herschel's, half-past five, where I can neither sleep nor lie idle.

"My Dear Fanny:—I believe I told you on Friday that I was going to finish the perusal of my astronomical verses to the great astronomer on Saturday.

* * * * * * *

"After tea Dr. Herschel proposed that we two should retire into a quiet room in order to resume the perusal of my work, in which no progress has been made since last December. The evening was finished very cheerfully; and we went to our bowers not much out of humor with each other or the world. . . . After dinner we all agreed to go to the terrace [at Windsor]—Mr., Mrs., and Miss H., with their nice little boy, and three young ladies. Here I met with almost everybody I wished and expected to see previous to the king's arrival.

* * * * * * *

"But now here comes Will, and I must get up, and make myself up to go down to the perusal of my last book, entitled Herschel. So good-morrow."

"Chelsea, Tuesday.

"Not a moment could I get to write till now. . . . I must tell you that Herschel proposed to me to go with him to the king's concert at night, he having permission to go when he chooses, his five nephews (Griesbachs) making a principal part of the band. 'And,' says he, 'I know you will be welcome.'"

An intimacy was gradually established between Herschel and Dr. Burney. They saw each other often at the meetings of the Royal Society, and Herschel frequently stayed at the doctor's house. "On the first evening Herschel spent at Chelsea, when I called for my Argand lamp, Herschel, who had not seen one of those lamps, was surprised at the great effusion of light, and immediately calculated the difference between that and a single candle, and found it sixteen to one."[25]

In 1793 we find Herschel as a witness for his friend James Watt, in the celebrated case of Watt vs. Bull, which was tried in the Court of Common Pleas. And from Muirhead's Life of Watt, it appears that Herschel visited Watt at Heathfield in 1810.

A delightful picture of the old age of Herschel is given by the poet Campbell,[26] whose nature was fitted to perceive the beauties of a grand and simple character like Herschel's:

"[Brighton], September 15, 1813.

. . . "I wish you had been with me the day before yesterday, when you would have joined me, I am sure, deeply in admiring a great, simple, good old man—Dr. Herschel. Do not think me vain, or at least put up with my vanity, in saying that I almost flatter myself I have made him my friend. I have got an invitation, and a pressing one, to go to his house; and the lady who introduced me to him, says he spoke of me as if he would really be happy to see me. . . . I spent all Sunday with him and his family. His son is a prodigy in sciences, and fond of poetry, but very unassuming. . . . Now, for the old astronomer himself. His simplicity, his kindness, his anecdotes, his readiness to explain—and make perfectly conspicuous too—his own sublime conceptions of the universe are indescribably charming. He is seventy-six, but fresh and stout; and there he sat, nearest the door, at his friend's house, alternately smiling at a joke, or contentedly sitting without share or notice in the conversation. Any train of conversation he follows implicitly; anything you ask he labors with a sort of boyish earnestness to explain.

"I was anxious to get from him as many particulars as I could about his interview with Buonaparte.[27] The latter, it was reported, had astonished him by his astronomical knowledge.

"'No,' he said, 'the First Consul did surprise me by his quickness and versatility on all subjects; but in science he seemed to know little more than any well-educated gentleman, and of astronomy much less for instance than our own king. His general air,' he said, 'was something like affecting to know more than he did know.' He was high, and tried to be great with Herschel, I suppose, without success; and 'I remarked,' said the astronomer, 'his hypocrisy in concluding the conversation on astronomy by observing how all these glorious views gave proofs of an Almighty Wisdom.' I asked him if he thought the system of Laplace to be quite certain, with regard to the total security of the planetary system from the effects of gravitation losing its present balance? He said, No; he thought by no means that the universe was secured from the chance of sudden losses of parts.

"He was convinced that there had existed a planet between Mars and Jupiter, in our own system, of which the little asteroids, or planetkins, lately discovered, are indubitably fragments; and 'Remember,' said he, 'that though they have discovered only four of those parts, there will be thousands—perhaps thirty thousand more—yet discovered.' This planet he believed to have been lost by explosion.

"With great kindness and patience he referred me, in the course of my attempts to talk with him, to a theorem in Newton's 'Principles of Natural Philosophy' in which the time that the light takes to travel from the sun is proved with a simplicity which requires but a few steps in reasoning. In talking of some inconceivably distant bodies, he introduced the mention of this plain theorem, to remind me that the progress of light could be measured in the one case as well as the other. Then, speaking of himself, he said, with a modesty of manner which quite overcame me, when taken together with the greatness of the assertion: 'I have looked further into space than ever human being did before me. I have observed stars, of which the light, it can be proved, must take two millions of years to reach this earth.'

"I really and unfeignedly felt at this moment as if I had been conversing with a supernatural intelligence. 'Nay, more,' said he, 'if those distant bodies had ceased to exist two millions of years ago, we should still see them, as the light would travel after the body was gone. . . .' These were Herschel's words; and if you had heard him speak them, you would not think he was apt to tell more than the truth.

"After leaving Herschel I felt elevated and overcome; and have in writing to you made only this memorandum of some of the most interesting moments of my life."

Campbell's conscientious biographer appears to have felt that the value of this charming account of his interview with Herschel was in its report of astronomical facts and opinions, and he adds a foot-note to explain that "Herschel's opinion never amounted to more than hypothesis having some degree of probability. Sir John Herschel remembers his father saying, 'If that hypothesis were true, and if the planet destroyed were as large as the earth, there must have been at least thirty-thousand such fragments,' but always as an hypothesis—he was never heard to declare any degree of conviction that it was so."

For us, the value of this sympathetic account of a day in Herschel's life is in its conception of the simplicity, the modesty, the "boyish earnestness," the elevation of thought and speech of the old philosopher; and in the impression made on the feelings, not the mind, of the poet, then thirty-five years old.

In a letter to Alison, Campbell reverts with great pleasure to the day spent with Herschel:

"Sydenham, December 12, 1813.

"My Dearest Alison:—

* * * * * * *

"I spent three weeks with my family at Brighton, in charming weather, and was much pleased with, as well as benefited by, the place. There I met a man with whom you will stare at the idea of my being congenial, or having the vanity to think myself so—the great Herschel. He is a simple, great being. . . . I once in my life looked at Newton's Principia, and attended an astronomical class at Glasgow; wonderful it seemed to myself, that the great man condescended to understand my questions; to become apparently earnest in communicating to me as much information as my limited capacity and preparation for such knowledge would admit. He invited me to see him at his own abode, and so kindly that I could not believe that it was mere good breeding; but a sincere wish to see me again. I had a full day with him; he described to me his whole interview with Buonaparte; said it was not true, as reported, that Buonaparte understood astronomical subjects deeply, but affected more than he knew.

"In speaking of his great and chief telescope, he said with an air, not of the least pride, but with a greatness and simplicity of expression that struck me with wonder, 'I have looked further into space than ever human being did before me. I have observed stars, of which the light takes two millions of years to travel to this globe.' I mean to pay him a reverential visit at Slough, as soon as my book is out, this winter."

* * * * * * *

In 1807 Carolina Herschel has this entry in her diary:

"October 4.—My brother came from Brighton. The same night two parties from the Castle came to see the comet, and during the whole month my brother had not an evening to himself. As he was then in the midst of polishing the forty-foot mirror, rest became absolutely necessary after a day spent in that most laborious work; and it has ever been my opinion that on the 14th of October his nerves received a shock of which he never got the better afterwards."

In the spring of 1808 he was quite seriously ill; but in May the observing went on again. In 1809 and 1810 his principal investigations were upon physical subjects (Newton's rings), and in 1811 the only long series of observations was upon the comet of that year. After 1811 the state of Herschel's health required that his observations should be much less frequent. Much of the time after 1811 he was absent, and his work at home consisted largely in arranging the results of his previous labors, and in computations connected with them. All through the years 1814 to 1822, Herschel's health was very feeble. The severe winter of 1813-14 had told materially upon him. In 1814, however, he undertook to repolish the forty-foot mirror, but was obliged to give it over.

He now found it necessary to make frequent little excursions for change of air and scene. His faithful sister remained at home, bringing order into the masses of manuscript, and copying the papers for the Royal Society.

She was sick at heart, fearing that each time she saw her brother it would be the last. In 1818 she says:

"Feb. 11, I went to my brother and remained with him till the 23d. We spent our time, though not in idleness, in sorrow and sadness. He is not only unwell, but low in spirits."

1818 (December 16), Herschel went to London to have his portrait painted by Artaud. While he was in London his will was made.[28]

In 1819 there is a glimmer of the old-time light. In a note Herschel says:

"Lina:—There is a great comet. I want you to assist me. Come to dine and spend the day here. If you can come soon after one o'clock, we shall have time to prepare maps and telescopes. I saw its situation last night. It has a long tail.

"July 4, 1819."

This note has been carefully kept by his sister, and on it she has written: "I keep this as a relic. Every line now traced by the hand of my dear brother becomes a treasure to me."

So the next three years passed away. Sir William[29] was daily more and more feeble. He spent his time in putting his works in order, but could devote only a few moments each day to this. His sister says:

"Aug. 11th, 12th, 13th, and 14th [1822], I went as usual to spend some hours of the forenoon with my brother. "Aug. 15th.—I hastened to the spot where I was wont to find him, with the newspaper which I was to read to him. But instead I found Mrs. Monson, Miss Baldwin, and Mr. Bulman, from Leeds, the grandson of my brother's earliest acquaintance in this country. I was informed my brother had been obliged to return to his room, whither I flew immediately. Lady H. and the housekeeper were with him, administering everything which could be thought of for supporting him. I found him much irritated at not being able to grant Mr. Bulman's request for some token of remembrance for his father. As soon as he saw me, I was sent to the library to fetch one of his last papers and a plate of the forty-foot telescope. But for the universe I could not have looked twice at what I had snatched from the shelf, and when he faintly asked if the breaking up of the Milky Way was in it, I said 'Yes,' and he looked content. I cannot help remembering this circumstance; it was the last time I was sent to the library on such an occasion. That the anxious care for his papers and workrooms never ended but with his life, was proved by his frequent whispered inquiries if they were locked and the key safe, of which I took care to assure him that they were, and the key in Lady Herschel's hands.

"After half an hour's vain attempt to support himself, my brother was obliged to consent to be put to bed, leaving no hope ever to see him rise again."

On the 25th of August, 1822, Herschel died peacefully at the age of eighty-four years.

His remains lie in the little church at Upton, near Windsor, where a memorial tablet has been erected by his son. The epitaph is as follows:[30]

H. S. E. Gulielmus Herschel Eques Guelphicus Hanoviæ natus Angliam elegit patriam Astronomis ætatis suæ præstantissimis Merito annumeratus Ut leviora sileantur inventa Planetam ille extra Saturni orbitam Primus detexit Novis artis adjumentis innixus Quæ ipse excogitavit et perfecit Cœlorum perrupit claustra Et remotiora penetrans et explorans spatia Incognitos astrorum ignes Astronomorum oculis et intellectui subjecit Qua sedulitate qua solertia Corporum et phantasmatum Extra systematis nostri fines lucentium Naturam indagaverit Quidquid paulo audacius conjecit Ingenita temperans verecundia Ultro testantur hodie æquales Vera esse quæ docuit pleraque Siquidem certiora futuris ingeniis subsidia Debitura est astronomia Agnoscent forte posteri Vitam utilem innocuam amabilem Non minus felici laborum exitu quam virtutibus Ornatam et vere eximiam Morte suis et bonis omnibus deflenda Nec tamen immatura clausit Die XXV Augusti A. D. CIƆIƆCCCXXII Ætatis vero suæ LXXXIV.

FOOTNOTES:

CHAPTER IV.

REVIEW OF THE SCIENTIFIC LABORS OF WILLIAM HERSCHEL.

In this chapter I shall endeavor to give such explanations as will enable the general reader to follow the course of discovery in each branch of astronomy and physics, regularly through the period of Herschel's life, and up to the state in which he left it.

A more detailed and precise account, which should appeal directly to the professional astronomer, will not be needed, since Arago has already fulfilled this want in his "Analyse de la vie et des travaux de Sir William Herschel," published in 1842. The few misconceptions there contained will be easily corrected by those to whom alone they are of consequence. The latter class of readers may also consult the abstracts of Herschel's memoirs, which have been given in "A Subject-index and a Synopsis of the Scientific Writings of Sir William Herschel," prepared by Dr. Hastings and myself, and published by the Smithsonian Institution.

An accurate sketch of the state of astronomy in England and on the Continent, in the years 1780-1820, need not be given. It will be enough if we remember that of the chief observatories of Europe, public and private, no one was actively devoted to such labors as were undertaken by Herschel at the very beginning of his career.

His observations on variable stars, indeed, were in the same line as those of Pigott; Flaugergues and Darquier, in France, had perhaps preceded him in minute scrutiny of the sun's surface, etc.; but, even in that department of observation, he at once put an immense distance between himself and others by the rapid and extraordinary advances in the size and in the excellence of his telescopes. Before his time the principal aids to observation were the Gregorian and Newtonian telescopes of Short, and the small achromatics of Dollond.[31]

We have seen, in what goes before, how his patient zeal had succeeded in improving upon these. There was no delay, and no rest. Steadily the art of making reflectors was urged forward, until he had finally in his hands the forty-foot telescope.

It must be admitted that this was the limit to which the manufacture of powerful telescopes could be pushed in his generation. The optical and mechanical difficulties which prevented a farther advance required time for their solution; and, indeed, some of these difficulties are scarcely solved at this day. It may fairly be said that no reflector larger than three feet in aperture has yet realized our expectations.

The Improvement of Telescopes and Optical Apparatus.

It will be of interest to give in this place some connected account of the large forty-foot reflector, of four feet aperture, made by Herschel. Its history extends from 1785 to 1811. Its manufacture was considered by his cotemporaries as his greatest triumph. As a machine, it was extremely ingenious in all its parts, as may be seen from the elaborate description and plates of it published in the Philosophical Transactions for 1795. One of its mirrors certainly had good definition, for, by means of it, the two small satellites of Saturn (Mimas and Enceladus) were discovered, and these discoveries alone would make it famous. Perhaps more was expected of it by the public in general than it absolutely performed. Its merits were after a while decried, and Herschel even felt obliged to state why he did not always employ it in his observations. His reasons were perfectly valid, and such as any one may understand. The time required to get so large a machine into working order was a serious tax; it required more assistants than his twenty-foot telescope, and he says, "I have made it a rule never to employ a larger telescope when a smaller will answer the purpose."

It still remains as a remarkable feat of engineering and an example of great optical and mechanical skill. It led the way to the large reflectors of Lord Rosse, some sixty years later, and several of the forty-foot telescopes of the present day even have done less useful work. Its great feat, however, was to have added two satellites to the solar system. From the published accounts of it the following is taken:

"When I resided at Bath I had long been acquainted with the theory of optics and mechanics, and wanted only that experience so necessary in the practical part of these sciences. This I acquired by degrees at that place, where in my leisure hours, by way of amusement, I made several two-foot, five-foot, seven-foot, ten-foot, and twenty-foot Newtonian telescopes, beside others, of the Gregorian form, of eight, twelve, and eighteen inches, and two, three, five, and ten feet focal length. In this way I made not less than two hundred seven-foot, one hundred and fifty ten-foot, and about eighty twenty-foot mirrors, not to mention the Gregorian telescopes.[32]

"The number of stands I invented for these telescopes it would not be easy to assign. . . . In 1781 I began to construct a thirty-foot aërial reflector, and having made a stand for it, I cast the mirror thirty-six inches in diameter. This was cracked in cooling. I cast it a second time, and the furnace I had built in my house broke."

Soon after, the Georgian planet was discovered, and this interrupted the work for a time.

"In the year 1783 I finished a very good twenty-foot reflector with a large aperture, and mounted it upon the plan of my present telescope. After two years' observation with it, the great advantage of such apertures appeared so clearly to me that I recurred to my former intention of increasing them still further; and being now sufficiently provided with experience in the work which I wished to undertake, the President of the Royal Society, who is always ready to promote useful undertakings, had the goodness to lay my design before the king. His Majesty was graciously pleased to approve of it, and with his usual liberality to support it with his royal bounty.

"In consequence of this arrangement I began to construct the forty-foot telescope about the latter end of 1785.[33] The woodwork of the stand and machines for giving the required motions to the instrument were immediately put in hand. In the whole of the apparatus none but common workmen were employed, for I made drawings of every part of it, by which it was easy to execute the work, as I constantly inspected and directed every person's labor; though sometimes there were not less than forty different workmen employed at the same time. While the stand of the telescope was preparing, I also began the construction of the great mirror, of which I inspected the casting, grinding, and polishing, and the work was in this manner carried on with no other interruption than that occasioned by the removal of all the apparatus and materials from where I then lived, to my present situation at Slough.

"Here, soon after my arrival, I began to lay the foundation upon which by degrees the whole structure was raised as it now stands, and the speculum being highly polished and put into the tube, I had the first view through it on February 19, 1787. I do not, however, date the completing of the instrument till much later. For the first speculum, by a mismanagement of the person who cast it, came out thinner on the centre of the back than was intended, and on account of its weakness would not permit a good figure to be given to it.

"A second mirror was cast January 26, 1788, but it cracked in cooling. February 16 we recast it, and it proved to be of a proper degree of strength. October 24 it was brought to a pretty good figure and polish, and I observed the planet Saturn with it. But not being satisfied, I continued to work upon it till August 27, 1789, when it was tried upon the fixed stars, and I found it to give a pretty sharp image. Large stars were a little affected with scattered light, owing to many remaining scratches on the mirror. August the 28th, 1789, having brought the telescope to the parallel of Saturn, I discovered a sixth satellite of that planet, and also saw the spots upon Saturn better than I had ever seen them before, so that I may date the finishing of the forty-foot telescope from that time."

Another satellite of Saturn was discovered with the forty-foot on the 17th of September (1789). It was used for various observations so late as 1811. On January 19, of that year, Herschel observed the nebula of Orion with it. This was one of his last observations.

The final disposition of the telescope is told in the following extract from a letter of Sir John Herschel's to Mr. Weld, Secretary of the Royal Society:

Collingwood, March 13, 1847.

. . . "In reply to your queries, respecting the forty-foot reflecting telescope constructed by my father, I have to state that King George III. munificently defrayed the entire cost of that instrument (including, of course, all preparatory cost in the nature of construction of tools, and of the apparatus for casting, grinding, and figuring the reflectors, of which two were constructed), at a total cost of £4,000. The woodwork of the telescope being so far decayed as to be dangerous, in the year 1839 I pulled it down, and piers were erected on which the tube was placed, that being of iron and so well preserved, that, although not more than one-twentieth of an inch thick, when in the horizontal position it sustained within it all my family, and continues to sustain inclosed within it, to this day, not only the heavier of the two reflectors, but also all the more important portions of the machinery. . . . The other mirror and the rest of the polishing apparatus are on the premises. The iron grinding tools and polishers are placed underneath the tube, let into the ground, and level with the surface of the gravelled area in which it stands.". . .

The closing of the tube was done with appropriate ceremony on New-Year's-Day, 1840, when, after a procession through it by the family at Slough, a poem, written by Sir John, was read, the machinery put into its present position, and the tube sealed.

The memoir on the forty-foot telescope shows throughout that Herschel's prime object was not the making of the telescope itself, but that his mind was constantly directed towards the uses to which it was to be put—towards the questions which he wished it to answer.

Again and again, in his various papers, he returns to the question of the limit of vision. As Bessel has said:

"The naked eye has its limit of vision in the stars of the sixth magnitude. The light of fainter stars than these does not affect the retina enough for them to be seen. A very small telescope penetrates to smaller, and, in general, without doubt, to more distant stars. A more powerful one penetrates deeper into space, and as its power is increased, so the boundaries of the visible universe are widened, and the number of stars increased to millions and millions. Whoever has followed the history of the series of Herschel's telescopes will have observed this. But Herschel was not content with the bare fact, but strove ever to know how far a telescope of a certain construction and size could penetrate, compared with the naked and unassisted eye. These investigations were never for the discovery of new facts concerning the working of his instruments; it was for the knowledge of the distribution of the fixed stars in space itself that he strove. . . . Herschel's instruments were designed to aid vision to the last extent. They were only secondarily for the taking of measures. His efforts were not for a knowledge of the motions, but of the constitution and construction of the heavenly bodies."

Besides the stands for his telescopes, which were both ingenious and convenient, Herschel devised many forms of apparatus for facilitating the art of observation. His micrometers for measuring position angles, his lamp micrometer, the method of limiting apertures, and the methods he used for viewing the sun may be mentioned among these.

Points in practical astronomy are considered all through the years of observation. A reference to his original papers will show how numerous, how varied, and how valuable these are. I cannot forbear quoting here the account of a precaution observed during his examination of the belts on Saturn (1794).

It is the most striking example of how fully Herschel realized that the eye of the observer is a material part of the optical apparatus of astronomy. Simple as this principle may appear, it was an absolute novelty in his day.

In making these observations, he says:

"I took care to bend my head so as to receive the picture of the belt in the same direction as I did formerly. This was a precaution that occurred to me, as there was a possibility that the vertical diameter of the retina might be more or less sensitive than the horizontal one."

Astronomers will recognize in this the first suggestion of the processes which have led to important results in the hands of Dr. Otto Struve and others in the comparison of the measures of double stars by different observers, each of whom has a personal habit of observation, which, if not corrected, may affect his results in the way which Herschel was striving to avoid.

Researches on the Relative Brightness of the Stars: Variable Stars.

No research of Herschel's was more laborious than the elaborate classification of the stars according to their comparative brightness, which he executed during the years 1796 to 1799. It was directly in the line of his main work—to find out the construction of the heavens.

His first paper had been upon the variable star Mira Ceti. Here was a sun, shining by its native brightness, which waxed and waned like the moon itself. This star is periodic. It is for a long period invisible to the unassisted eye. Then it can just be seen, and increases in brightness for a little over a month, and attains a maximum brilliancy. From this it decreases for nearly three months, and after becoming invisible, remains so for five or six months. Its whole period is about 333 days. Are all other stars constant in brightness? The example of Mira Ceti and of other known variables makes this at least doubtful. But the sun itself may vary for all that we know. It is a simple star like the rest.

This question of variability in general is an important one, then. It can only be tested by making accurate catalogues of the relative brilliance of stars at various times, and by comparing these. No such general catalogue existed before Herschel's time, and led by the discrepancies in isolated cases, which he found between his own estimates and those of his predecessors, he made from observation a series of four catalogues, in which were set down the order of sequence of the stars of each constellation.

The method adopted by Herschel was perfectly simple in principle, though most laborious in practice. Suppose any number of stars, A, B, C, D, E, . . . etc., near enough to each other to be well compared. The process consists simply in writing down the names of the stars, A, B, C, etc., in the order of their relative brightness. Thus if for a group of eight stars we have found at one epoch A, B, C, D, E, F, G, H, and if at another time the order was A, B, C, D, F, E, G, H, symptoms of variability are pointed out. Repeated observations, where the same star is found in different sequences, will decide the question. Thus, for the stars visible to the naked eye, we know exactly the state of the sky in Herschel's day, now nearly a century ago. Any material change cannot escape us. These catalogues have been singularly overlooked by the observers of our generation who have followed this branch of observation, and it was not till 1876 that they received proper attention and a suitable reduction (at the hands of Mr. C. S. Pierce).

We owe to Herschel the first trustworthy account of the stars visible to the naked eye, and since the date of his labors (about 1800) we have similar views published by Argelander (1839), Heis (1848), Argelander and Schönfeld (1857), Gould (1860 and 1872), and Houzeau (1875). Thus his labors have been well followed up.

In the prosecution of this work Herschel found stars whose light was progressively diminishing, others which regularly increased, one star whose light periodically varies (α Herculis), and at least one star (55 Herculis) which has utterly disappeared. On October 10, 1781, and April 11, 1782, he observed this latter star, but in May, 1791, it had totally vanished. There was no trace remaining.

The discovery of the variability of α Herculis was a more important one than would at first sight appear. Up to that time the only variable stars known were seven in number. Their-periods were four hundred and ninety-four, four hundred and four, three hundred and thirty-four, seven, six, five, and three days. These periods seemed to fall into two groups, one of from three hundred to five hundred days, the other comparatively much shorter, of three to seven days. α Herculis came to occupy the middle place between these groups, its period being about sixty days.

The cause of these strange and regular variations of brightness was supposed by Herschel to be the rotation of the star bodily on an axis, by which revolution different parts of its surface, of different brilliancy, were successively and periodically presented to us. This explanation it might have been difficult to receive, when the periods of the known variables were so markedly various in length. His own discovery came to bridge over the interval, and quite confirmed him in his belief. He returned to the subject of the revolution of stars about their axes again and again, and connected it with the revolution of satellites.

He found that the satellites of Jupiter and one of Saturn's periodically changed in brightness, and by quite simple means showed that their periods of rotation were at least approximately the same as their periods of revolution about their primaries. In this case, as in every other, he considered a discovery in each and every one of its possible bearings. There are no instances where he has singularly overlooked the consequences of his observations.

Researches on Double Stars.

The double stars were the subject of Herschel's earliest and of his latest papers. In 1782 he published his "Catalogue of Double Stars," and his last published memoir (1822) was on the same subject.

The question of determining the parallax of stars first brought Herschel to the discovery of double stars. If two stars, A and B, appear very close together, and if, in reality, the star B is very many times more distant from the earth than A, although seen along the same line of sight, then the revolution of the earth in its orbit will produce changes in the relative situation of A and B, and, in fact, B will describe a small orbit about A, due to this revolution. This idea had been proposed by Galileo, and measures on this plan had been made by Long, with negative results. But Herschel, in reviewing their work, declares that the stars chosen by Long were not suitable to the purpose. It is necessary, among other things, to the success of this method, that it should be certain that the star B is really very much more distant than the star A. The only general test of the distance of stars is their brilliancy, and Herschel decided to use only stars for this research which had two components very greatly different in brightness. A must be very bright (and presumably near to us), and B must be very close to A, and very faint (and thus, presumably, very distant).

It was in the search for such pairs of stars that the Catalogue of Double Stars (1782) was formed. Herschel's first idea of a double star made such pairs as he found, to consist of two stars accidentally near to each other. A was near to us, and appeared projected in a certain place on the celestial sphere. B was many times more distant, but, by chance, was seen along the same line, and made with A an optical double. If the two stars were at the same distance from the earth, if they made part of the same physical system, if one revolved around the other, then this method of gaining a knowledge of their distance failed. Even in his first memoir on the subject, a surmise that this latter state might occur in some cases, was expressed by Herschel. The notes on some of the pairs declare that a motion of one of them was suspected. But this motion might be truly orbital—of one star about the other as a centre—or it might simply be that one star was moving by its own proper motion, and leaving the other behind. It was best to wait and see. The first Catalogue of Double Stars contained two hundred and three instances of such associations. These were observed from time to time, and new pairs discovered. The paper of Michell, "An Inquiry into the probable Parallax and Magnitude of the Fixed Stars, from the Quantity of Light which they Afford, and the Particular Circumstances of their Situation" (1767), was read and pondered. By 1802 Herschel had become certain that there existed in the heavens real pairs of stars, both at the same distance from the earth, which were physically connected with each other. The arguments of Michell have been applied by Bessel to the case of one of Herschel's double stars, in much the same order in which the argument ran in Herschel's own mind, as follows:

The star Castor (α Geminorum) is a double star, where A is of the second, and B of the fourth, magnitude. To the naked eye these two appear as one star. With a telescope this is seen to be two stars, some 5″ apart. In the whole sky there are not above fifty such stars as the brighter of the two, and about four hundred of the brilliancy of B. These fifty and four hundred stars are scattered over the vault of heaven, almost at random. No law has yet been traced by which we can say that here or here there shall be a bright star like A, or a fainter one like B. In general the distribution appears to be fortuitous. How then can we account for one of the four hundred stars like B placed so close to one of the fifty like A?

The chances are over four hundred thousand to one that the association in position is not accidental. This argument becomes overwhelming when the same association is found in many other cases. There were two hundred and three doubles in the Catalogue of 1782 alone, and many thousands are now known.

By a process like this, Herschel reached his grand discovery of true binary systems, where one sun revolves about another. For he saw that if the two stars are near together in space, they could not stand still in face of each other, but that they must revolve in true orbits. Here was the discovery which came to take the place of the detection of the parallaxes of the fixed stars.

He had failed in one research, but he was led to grand conclusions. Was the force that these distant pairs of suns obeyed, the force of gravitation? This he could not settle, but his successors have done so. It was not till about 1827 that Savary, of the Paris Observatory, showed that one of Herschel's doubles was subjected to the law of gravitation, and thus extended the power of this law from our system to the universe at large. Herschel himself lived to see some of his double stars perform half a revolution.

Of Herschel's discoveries, Arago thinks this has "le plus d'avenir." It may well be so. The laws which govern our solar system have been extended, through his researches, to regions of unknown distance. The binary stars will afford the largest field for research into the laws which govern them, and together with the clusters and groups, they will give a firm basis by which to study the distribution of stars in general, since here we have the great advantage of knowing, if not the real distance of the two stars from the earth, at least that this distance is alike for both.

Researches on Planets and Satellites.

After Herschel's first publication on the mountains of the Moon (1780), our satellite appears to have occupied him but little. The observation of volcanoes (1787) and of a lunar eclipse are his only published ones. The planets Mercury, Venus, Mars, and Jupiter, although they were often studied, were not the subjects of his more important memoirs. The planet Saturn, on the contrary, seems never to have been lost sight of from the time of his first view of it in 1772.

The field of discovery always appears to be completely occupied until the advent of a great man, who, even by his way of putting old and familiar facts, shows the paths along which discoveries must come, if at all. This faculty comes from profound reflection on the nature of the subject itself, from a sort of transmuting power which changes the words of the books into the things of reality. Herschel's paper on Saturn, in 1790, is an admirable example of this.

Herschel's observations on Saturn began in 1772. From 1790 to 1808 he published six memoirs on the figure, the ring, and the satellites of this planet. The spheroidal shape of the ball was first discovered by him, and we owe much of our certain knowledge of the constitution of the rings to his work. The sixth and seventh satellites, Mimas and Enceladus, were discovered by him in 1789. The periods of rotation of the ball and of the ring were also fixed. In his conclusions as to the real figure of the rings, there is a degree of scientific caution which is truly remarkable, and which to-day seems almost excessive.

In his paper of 1792, Herschel shows that the most distant satellite of Saturn—Japetus—turns once on its axis in each revolution about its primary, just as our moon does. He says of this:

"I cannot help reflecting with some pleasure on the discovery of an analogy which shows that a certain uniform plan is carried on among the secondary planets of our solar system; and we may conjecture that probably most of the satellites are governed by the same law; especially if it be founded on such a construction of their figure as makes them more ponderous towards their primary planets."

I believe the last suggestion to have been the first statement of the possible arrangement of matter in satellites, which was afterwards so forcibly maintained by Hansen in his theory of the moon. Hansen's researches show the consequences of such an arrangement, although they do not prove its existence.

It should be recorded that the explanation which is to-day received of the belts and bands upon Jupiter, is, I believe, first found in Herschel's memoir on Venus (1793). His memoir of 1797, on the changeable brightness of the satellites of Jupiter, has already been referred to. The times of the rotation of the satellites on their axes was first determined by Herschel from these observations, which also contain accounts of the curious, and as yet unexplained, phenomena attending their appearances on the disc of the planet.

Herschel discovered in January, 1787, the two brighter satellites of Uranus, now called Oberon and Titania. They are among the faintest objects in the solar system. A later discussion of all his observations led him to the belief that there were four more, and he gives his observations and computations in full. He says that of the existence of additional satellites he has no doubt. Of these four, three were exterior to the most distant satellite Oberon, the other was "interior" to Titania.

It was not until 1834 that even Oberon and Titania were again observed (by Sir John Herschel) with a telescope of twenty feet, similar to that which had discovered them, and not until 1847 was the true state of this system known, when Mr. Lassell discovered Ariel and Umbriel, two satellites interior to Titania, neither of which was Herschel's "interior" satellite. In 1848 and later years Mr. Lassell, by the aid of telescopes constructed by himself, fully settled the fact that only four satellites of this planet existed. In 1874 I examined the observations of Herschel on his supposed "interior" satellite, thinking that it might be possible that among the very few glimpses of it which he recorded, some might have belonged to Ariel and some to Umbriel, and that by combining rare and almost accidental observations of two satellites which really existed, he had come to announce the existence of an "interior" satellite which had no existence in fact. Such I believe to be the case. In 1801, April 17, Herschel describes an interior satellite in the position angle 189°, distant 18″ from the planet. At that instant Umbriel, one of Mr. Lassell's satellites, was in the position 191°, and distant 21″ from Uranus, in the most favorable position for seeing it. The observation of 1794, March 27, may belong to Ariel. At the best the investigation is of passing interest only, and has nothing to do with the question of the discovery of the satellites. Herschel discovered the two brighter ones, and it was only sixty years later that they were properly re-observed by Mr. Lassell, who has the great honor of having added as many more, and who first settled the vexed question of satellites exterior to Oberon, and this with a reflecting telescope made by himself, which is unequalled by any other of its dimensions.

Researches on the Nature of the Sun.

In the introduction to his paper on the Nature and Construction of the Sun and Fixed Stars (1795), Herschel recounts what was known of the nature of the sun at that time. Newton had shown that it was the centre of the system; Galileo and his successors had determined its rotation, the place of its equator, its real diameter, magnitude, density, distance, and the force of gravity on its surface. He says:

"I should not wonder if, considering all this, we were induced to think that nothing remained to be added; and yet we are still very ignorant in regard to the internal construction of the sun." "The spots have been supposed to be solid bodies, the smoke of volcanoes, the scum floating on an ocean of fluid matter, clouds, opaque masses, and to be many other things." "The sun itself has been called a globe of fire, though, perhaps, metaphorically." "It is time now to profit by the observations we are in possession of. I have availed myself of the labors of preceding astronomers, but have been induced thereto by my own actual observation of the solar phenomena."

Herschel then refers to the theories advanced by his friend, Prof. Wilson, of Glasgow, in 1774. Wilson maintained that the spots were depressions below the sun's atmosphere, vast hollows as it were, at the bases of which the true surface of the sun could be seen.

The essence of his theory was the existence of two different kinds of matter in the sun: one solid and non-luminous—the nucleus—the other gaseous and incandescent—the atmosphere. Vacant places in the atmosphere, however caused, would show the black surface of the solid mass below. These were the spots. No explanation could be given of the faculæ, bright streaks, which appear on the sun's surface from time to time; but his theory accounted for the existence of the black nuclei of the spots, and for the existence of the penumbræ about these. The penumbra of a spot was formed by the thinner parts of the atmosphere about the vacancy which surrounded the nucleus.

This theory of Wilson's was adopted by Herschel as a basis for his own, and he brought numerous observations to confirm it, in the modified shape which he gave to it.

According to Herschel, the sun consisted of three essentially different parts. First, there was a solid nucleus, non-luminous, cool, and even capable of being inhabited. Second, above this was an atmosphere proper; and, lastly, outside of this was a layer in which floated the clouds, or bodies which gave to the solar surface its intense brilliancy:

"According to my theory, a dark spot in the sun is a place in its atmosphere which happens to be free from luminous decompositions" above it.

The two atmospheric layers, which will be of varying thickness about a spot, will account for all the shades of darkness seen in the penumbra. Ascending currents from the solar surface will elevate certain regions, and may increase the solar activity near by, and will thus give rise to faculæ, which Herschel shows to be elevated above the general surface. It will not be necessary to give a further account of this theory. The data in the possession of the modern theorist is a thousand-fold that to be derived from Herschel's observations, and, while the subject of the internal construction of the sun is to-day unsettled, we know that many important, even fundamental, portions of his theory are untenable. A remark of his should be recorded, however, as it has played a great part in such theories:

"That the emission of light must waste the sun, is not a difficulty that can be opposed to our hypothesis. Many of the operations of Nature are carried on in her great laboratory which we cannot comprehend. Perhaps the many telescopic comets may restore to the sun what is lost by the emission of light."

Arguments in favor of the habitability of both sun and moon are contained in this paper; but they rest more on a metaphysical than a scientific basis, and are to-day justly forgotten.

Researches on the Motion of the Sun and of the Solar System in Space.

In 1782 Herschel writes, in regard to some of his discoveries of double stars:

"These may serve another very important end. I will just mention it, though it is foreign to my present purpose. Several stars of the first magnitude have been observed or suspected to have a proper motion; hence we may surmise that our sun, with all its planets and comets, may also have a motion towards some particular point of the heavens. . . . If this surmise should have any foundation, it will show itself in a series of some years in a kind of systematical parallax, or change, due to the motion of the whole solar system."

In 1783 he published his paper On the Proper Motion of the Solar System, which contained the proofs of his surmises of a year before. That certain of the stars had in fact a proper motion had been well established by the astronomers of the eighteenth century. After all allowances had been made for the effects of precession and other displacements of a star's position which were produced by motions of the earth, it was found that there were still small outstanding differences which must be due to the motion of the star itself—its proper motion. The quantity of this motion was not well known for any star when Herschel's researches began. Before they were concluded, however, Maskelyne had deduced the proper motions of thirty-six stars—the fundamental stars, so called—which included in their number Sirius, Procyon, Arcturus, and generally the brightest stars.

It is à priori evident that stars, in general, must have proper motions, when once we admit the universality of gravitation. That any fixed star should be entirely at rest would require that the attractions on all sides of it should be exactly balanced. Any change in the position of this star would break up this balance, and thus, in general, it follows that stars must be in motion, since all of them cannot occupy such a critical position as has to be assumed. If but one fixed star is in motion, this affects all the rest, and we cannot doubt but that every star, our sun included, is in motion by an amount which varies from small to great. If the sun alone had a motion, and the other stars were at rest, the consequence of this would be that all the fixed stars would appear to be retreating en masse from that point in the sky towards which we were moving. Those nearest us would move more rapidly, those more distant less so. And in the same way, the stars from which the solar system was receding would seem to be approaching each other. If the stars, instead of being quite at rest, as just supposed, had motions proper to themselves, then we should have a double complexity. They would still appear to an observer in the solar system to have motions, and part of these motions would be truly proper to the stars, and part would be due to the advance of the sun itself in space.

Observations can show us only the resultant of these two motions. It is for reasoning to separate this resultant into its two components. At first the question is to determine whether the results of observation indicate any solar motion at all. If there is none, the proper motions of stars will be directed along all possible lines. If the sun does truly move, then there will be a general agreement in the resultant motions of the stars near the ends of the line along which it moves, while those at the sides, so to speak, will show comparatively less systematic effect. It is as if one were riding in the rear of a railway train and watching the rails over which it has just passed. As we recede from any point, the rails at that point seem to come nearer and nearer together.

If we were passing through a forest, we should see the trunks of the trees from which we were going apparently come nearer and nearer together, while those on the sides of us would remain at their constant distance, and those in front would grow further and further apart.

These phenomena, which occur in a case where we are sensible of our own motion, serve to show how we may deduce a motion, otherwise unknown, from the appearances which are presented by the stars in space.

In this way, acting upon suggestions which had been thrown out previously to his own time by Lambert, Mayer, and Bradley, Herschel demonstrated that the sun, together with all its system, was moving through space in an unknown and majestic orbit of its own. The centre round which this motion is directed cannot yet be assigned. We can only know the point in the heavens towards which our course is directed—"the apex of solar motion."

By a study of the proper motions assigned by Maskelyne to the brighter stars, Herschel was able to define the position of the solar apex with an astonishing degree of accuracy. His calculations have been several times repeated with the advantage of modern analytical methods, and of the hundred-fold material now at our disposition, but nothing essential has been added to his results of 1805, which were based upon such scanty data; and his paper of 1782 contains the announcement of the discovery itself.

His second paper on the Direction and Velocity of the solar system (1805) is the best example that can possibly be given of his marvellous skill in reaching the heart of a matter, and it may be the one in which his philosophical powers appear in their highest exercise. For sustained reflection and high philosophic thought it is to be ranked with the researches of Newton in the Principia.

Researches on the Construction of the Heavens.

Herschel's papers on the Construction of the Heavens, as he named it, extended over his whole scientific life. By this he specially means the method according to which the stars, the clusters, the nebulæ, are spread through the regions of space, the causes that have led to this distribution, and the laws to which it is subjected.

No single astronomical fact is unimportant in the light which it may throw on the scheme of the whole, and each fact is to be considered in this light. As an instance: his discovery of the variable star α Herculis, which has a period of sixty days, was valuable in itself as adding one more to the number of those strange suns whose light is now brighter, now fainter, in a regular and periodic order. But the chief value of the discovery was that now we had an instance of a periodic star which went through all its phases in sixty days, and connected, as it were, the stars of short periods (three to seven days) with those of very long ones (three hundred to five hundred days), which two groups had, until then, been the only ones known. In the same way all his researches on the parallaxes of stars were not alone for the discovery of the distance of any one or two single stars, but to gain a unit of celestial measure, by means of which the depths of space might be sounded.

Astronomy in Herschel's day considered the bodies of the solar system as separated from each other by distances, and as filling a cubical space. The ideas of near and far, of up and down, were preserved, in regard to them, by common astronomical terms. But the vast number of stars seemed to be thought of, as they appear in fact to exist, lying on the surface of a hollow sphere. The immediate followers of Bradley used these fixed stars as points of reference by which the motions within the solar system could be determined, or, like Lacaille and Lalande, gathered those immense catalogues of their positions which are so indispensable to the science. Michell and Herschel alone, in England, occupied their thoughts with the nature and construction of the heavens—the one in his study, the other through observation.[34] They were concerned with all three of the dimensions of space.

In his memoir of 1784, Herschel says:

"Hitherto the sidereal heavens have, not inadequately for the purpose designed, been represented by the concave surface of a sphere, in the centre of which the eye of an observer might be supposed to be placed.

"It is true the various magnitudes of the fixed stars even then plainly suggested to us, and would have better suited, the idea of an expanded firmament of three dimensions; but the observations upon which I am now going to enter still farther illustrate and enforce the necessity of considering the heavens in this point of view. In future, therefore, we shall look upon those regions into which we may now penetrate by means of such large telescopes, as a naturalist regards a rich extent of ground or chain of mountains containing strata variously inclined and directed, as well as consisting of very different materials. The surface of a globe or map, therefore, will but ill delineate the interior parts of the heavens."

Herschel's method of study was founded on a mode of observation which he called star-gauging. It consisted in pointing a powerful telescope toward various parts of the heavens, and ascertaining by actual count how thick the stars were in each region. His twenty-foot reflector was provided with such an eye-piece that, in looking into it, he saw a portion of the heavens about 15′ in diameter. A circle of this size on the celestial sphere has about one quarter the apparent surface of the sun, or of the full moon. On pointing the telescope in any direction, a greater or less number of stars were visible. These were counted, and the direction in which the telescope pointed was noted. Gauges of this kind were made in all parts of the sky, and the results were tabulated in the order of right ascension.

The following is an extract from the gauges, and gives the average number of stars in each field at the points noted in right ascension and north polar distance:

N. P. D. N. P. D.

R. A. 78° to 80°. R. A. 92° to 94°.

No. of Stars. No. of Stars.

H.M. H.M.

11 6 3.1 1510 9.4

1231 3.4 1522 10.6

1244 4.6 1547 10.6

1249 3.9 16 8 12.1

13 5 3.8 16 25 13.6

1430 3.6 1637 18.6

In this small table, it is plain that a different law of clustering or of distribution obtains in the two regions. Such differences are still more marked, if we compare the extreme cases found by Herschel, as R. A. = 19^h 41^m, N. P. D. = 74° 33′, number of stars per field = 588; and R. A. = 16^h 10^m, N. P. D. = 113° 4′, number of stars = 1.1.

The number of stars in certain portions is very great. For example, in the Milky Way, near Orion, six fields of view promiscuously taken gave 110, 60, 70, 90, 70, and 74 stars each, or a mean of 79 stars per field. The most vacant space in this neighborhood gave 60 stars. So that as Herschel's sweeps were two degrees wide in declination, in one hour (15°) there would pass through the field of his telescope 40,000 or more stars. In some of the sweeps this number was as great as 116,000 stars in a quarter of an hour.

When Herschel first applied his telescope to the Milky Way, he believed that it completely resolved the whole whitish appearance into small stars. This conclusion he subsequently modified. He says:

"It is very probable that the great stratum called the Milky Way is that in which the sun is placed, though perhaps not in the very centre of its thickness.

"We gather this from the appearance of the Galaxy, which seems to encompass the whole heavens, as it certainly must do if the sun is within it. For, suppose a number of stars arranged between two parallel planes, indefinitely extended every way, but at a given considerable distance from each other; and calling this a sidereal stratum, an eye placed somewhere within it will see all the stars in the direction of the planes of the stratum projected into a great circle, which will appear lucid on account of the accumulation of the stars, while the rest of the heavens, at the sides, will only seem to be scattered over with constellations, more or less crowded according to the distance of the planes, or number of stars contained in the thickness or sides of the stratum.

"If the eye were placed somewhere without the stratum, at no very great distance, the appearance of the stars within it would assume the form of one of the smaller circles of the sphere, which would be more or less contracted according to the distance of the eye; and, if this distance were exceedingly increased, the whole stratum might at last be drawn together into a lucid spot of any shape, according to the length, breadth, and height of the stratum.

"Suppose that a smaller stratum should branch out from the former in a certain direction, and that it also is contained between two parallel planes, so that the eye is contained within the great stratum somewhere before the separation, and not far from the place where the strata are still united. Then this second stratum will not be projected into a bright circle like the former, but it will be seen as a lucid branch proceeding from the first, and returning into it again at a distance less than a semicircle. If the bounding surfaces are not parallel planes, but irregularly curved surfaces, analogous appearances must result."

The Milky Way, as we see it, presents the aspect which has been just accounted for, in its general appearance of a girdle around the heavens and in its bifurcation at a certain point, and Herschel's explanation of this appearance, as just given, has never been seriously questioned. One doubtful point remains: are the stars scattered all through space? or are they near its bounding planes, or clustered in any way within this space so as to produce the same result to the eye as if uniformly distributed?

Herschel assumed that they were nearly equably arranged all through the space in question. He only examined one other arrangement, viz., that of a ring of stars surrounding the sun, and he pronounced against such an arrangement, for the reason that there is absolutely nothing in the size or brilliancy of the sun to cause us to suppose it to be the centre of such a gigantic system. No reason, except its importance to us personally, can be alleged for such a supposition. Every star will have its own appearance of a Galaxy or Milky Way, which will vary according to the situation of the star.

Such an explanation will account for the general appearances of the Milky Way and of the rest of the sky, supposing the stars equally or nearly equally distributed in space. On this supposition, the system must be deeper where the stars appear most numerous.

Herschel endeavored, in his early memoirs, to explain this inequality of distribution on the fundamental assumption that the stars were nearly equably distributed in space. If they were so distributed, then the number of stars visible in any gauge would show the thickness of the stellar system in the direction in which the telescope was pointed. At each pointing, the field of view of the instrument includes all the visible stars situated within a cone, having its vortex at the observer's eye, and its base at the very limits of the system, the angle of the cone (at the eye) being 15′. Then the cubes of the perpendiculars let fall from the eye, on the plane of the bases of the various visual cones, are proportional to the solid contents of the cones themselves, or, as the stars are supposed equally scattered within all the cones, the cube roots of the numbers of stars in each of the fields express the relative lengths of the perpendiculars. A section of the sidereal system along any great circle can be constructed from the data furnished by the gauges in the following way:

The solar system is within the mass of stars. From this point lines are drawn along the different directions in which the gauging telescope was pointed. On these lines are laid off lengths proportional to the cube roots of the number of stars in each gauge. The irregular line joining the terminal points will be approximately the bounding curve of the stellar system in the great circle chosen. Within this line the space is nearly uniformly filled with stars. Without it is empty space. A similar section can be constructed in any other great circle, and a combination of all such would give a representation of the shape of our stellar system. The more numerous and careful the observations, the more elaborate the representation, and the 863 gauges of Herschel are sufficient to mark out with great precision the main features of the Milky Way, and even to indicate some of its chief irregularities.