Editorial note — APPENDIX.

A24. Galileo Galilei was a strenuous defender of the system of Copernicus; for which he was condemned by the inquisition, in the year 1635, under Pope Urban VIII. This extraordinary man was a native of Florence, and born in 1564. He died in 1642, aged seventy-eight years.

W. B.

A25. It has been since ascertained that Saturn has seven satellites, as is more particularly mentioned in the subsequent note. W. B.

A26. It was about six years after the delivery of this oration, (viz. on the 13th of March, 1781,) that Herschel discovered the Georgium Sidus. And nearly eight years and an half after this first discovery, he made two others: on the 28th of August, 1789, he was enabled to ascertain, by means of his telescope of forty feet focal length, that Saturn has a sixth satellite; and, on the 17th of September following, he found that he has a seventh. The same celebrated astronomer has since made several important discoveries. Thus, under the liberal patronage of his sovereign, has the great Herschel succeeded, by his extraordinary skill and industry in the making of very large specula, in constructing telescopes, which, in the words of the learned Mr. Vince, “have opened new views of the heavens, and penetrated into the depths of the universe; unfolding scenes which excite no less our wonder than our admiration.”

Many important discoveries (some of which are noticed in the foregoing pages of these memoirs) have been made by other eminent astronomerseminent astronomers, since the date of Dr. Rittenhouse’s Oration; some of them, indeed, since his decease; among which are the discoveries of three new planets. W. B.

A27. The celebrated Huygens, who, in his Latin works, is styled Hugenius. W. B.

A28. Among the many eminent astronomers in the sixteenth and seventeenth centuries, mentioned by Mr. Lalande, in his Astronomie, with interesting particulars concerning most of them, the only notice he there takes of his ingenious countryman, who endeavoured to establish the theory of Vortices which he had projected, is in these words: “Descartes (René,) né en Touraine en 1596, mort à Stockholm en 1650. Sa vie a été écrite fort au long par Baillet, à Paris, 1691, in 4^o.” W. B.

A29. The philosophy of Aristotle retained terms so very obscure, that it seems the Devil himself did not understand, or at least could not explain them; otherwise we can hardly suppose, that, when the good patriarch of Venice had summoned his attendance for this very purpose, he would have been so rude as to put him off with an answer not only unintelligible but inarticulate. See Bayle, in Art. Barbaro.

A30. Alluding to the experiments made in France, for determining the velocity of light; which, though unsuccessful, discovered a noble philosophical spirit.

A31. This prodigious velocity of light can be no argument against its materiality, as will appear from the following considerations. The greatest velocity which we can communicate to any body, is that of a cannon-ball, impelled by gun-powder; this may be at the rate of about 20 miles in a minute of time. The planet Saturn moves about 360 miles in a minute, that is 18 times swifter than a cannon-ball; and the comet of 1680, in its perihelion, moved near 56.66 times swifter than Saturn, or 990.5 times swifter than a cannon-ball. Now these are material bodies, moving with very various, and all of them exceedingly great velocities; and no reason appears why the last mentioned velocity should be the utmost limit, beyond which nature cannot proceed; or that some other body may not move 7 or 8 hundred times swifter than a comet, as light is found to do.

That the different refrangibility of the rays of light, on which their colours depend, arises from their different velocities, seems so natural a conjecture, that it has perhaps occurred to every one who has thought on this subject. To this there are three principal objections. The first is, that, according to this hypothesis, when the satellites of Jupiter are eclipsed, their colour ought to change, first to a green and then to a blue, before their light becomes extinct; which is contrary to experience. But this objection appears to me of no weight; for we do not lose sight of the satellite because there is no light coming from thence to the eye, but because there is not light enough to render it visible. Therefore at the time a satellite disappears, there is still light of all colours arriving at the eye: and though the blue light should predominate on account of its slower progress, yet the red may predominate on another account; for along the edge of Jupiter’s shadow, as it passes over the satellite, a greater proportion of red light, than of blue, will be thrown by the refraction of Jupiter’s atmosphere. The second objection is, that since the velocity of the earth in its orbit, causes an aberration of about 20 seconds in the place of a star, if the different colours of light depended on different velocities, the aberration of blue light ought proportionably to exceed that of red light, which would give such an oblong form to a fixed star as might be discovered with a good telescope. This objection is of no more force than the former. The effect ought indeed to follow, but not in a sensible quantity; for at the altitude of 70 degrees, the apparent place of a fixed star is likewise removed 20 seconds by refraction, and the very same separation of the rays must take place; yet this I think is not discoverable with the best telescope. Perhaps by uniting these two equal causes, which may be readily done, and thereby doubling the effect, it may become sensible.

The third objection arises from that curious discovery of Dollond, by which we are enabled so greatly to improve refracting telescopes. And this objection I shall for the present leave in its full force; as well against the above hypothesis, as against every other which I have seen for the same purpose.

A32. Mars appears to be surrounded by a very great and dense atmosphere.

A33. Dr. Herschel discovered, in the year 1789, (fourteen years after the delivery of this Oration,) two other satellites of Saturn. These are the innermost of his (now) seven secondary planets.

W. B.

A34. In 745, Virgilus, bishop of Saltzburg, having publicly asserted in some of his sermons, that there were antipodes, he was charged with heresy, by Boniface, bishop of Mentz, and cited to appear before the Pope, who recommended the hearing of the cause to Utilo, King of Bohemia, and at the same time wrote to him in favour of Boniface. The event was, the bishop of Saltzburg lost his cause, and was condemned for heresy.

A35. It has been shewn, in a preceding note, how much the means of communicating between distant regions, separated by seas, ware facilitated by the discovery and use of the Compass: but those means have been still further and very greatly improved, since the introduction of the use of the Quadrant at sea, especially that called Hadley’s Quadrant.

The true inventor of the reflecting Quadrant was Dr. Robert Hook, a very ingenious English mathematician and philosopher, who died in the year 1702, at the age of sixty-seven years. This instrument, now commonly styled Hadley’s, was afterwards rendered much more complete than Dr. Hook’s invention had made it, by Sir Isaac Newton: but our modern artists, more skilful than those of former times, as Mr. Lalande has observed, have profited of the ideas of the great Newton himself, on the subject; and among the later improvers of the Sea Quadrant, or Octant, is Mr. Hadley, whose name the instrument usually bears.

It would, however, be doing an act of injustice to the memory of an American who possessed an extraordinary genius, to omit, in the course of these memoirs, some notice of his merits in relation to this matter. Mr. Thomas Godfrey, a native of Pennsylvania, is said to have turned his attention to this subject, so early as the year 1730; and in the Transactions of the Royal Society of London, No. 435, will be found, an “Account of Mr. Thomas Godfrey’s Improvement of Davis’s Quadrant transferred to the Mariner’s Bow,” drawn up by James Logan, Esq. formerly of Philadelphia, a gentleman of extensive learning, and a very eminent mathematician, Mr. Godfrey is stated to have “sent the instrument (which he had constructed) to be tried at sea by an acquaintance of his, an ingenious navigator, in a voyage to Jamaica, who shewed it to a captain of a ship there, just going for England; by which means, it came to the knowledge of Mr. Hadley, though perhaps without his being toldtold the name of the real inventor.” [See The American Magazine, for July 1758.] In a letter, dated at Philadelphia the 25th of May, 1732, Mr. Logan, who very ably as well as meritoriously patronized Godfrey, communicated to the celebrated Dr. Edmund Halley a detailed account and description of the improved Sea-Quadrant constructed by that ingenious citizen of America, of which his patron confidently believed him to be the original inventor. On the 28th of June, 1734, a further account of Godfrey’s invention was drawn up by Mr. Logan, and subscribed with his name; which, it is presumed, was also communicated to the Royal Society: and on the 9th of November, in the same year, Mr. Godfrey transmitted an account of it, draughted and signed by himself, to the same learned body. The whole of these interesting letters, with some accompanying observations on the subject, are published in the valuable Magazine just referred to, and in the one for the succeeding month.

In the Transactions of the Royal Society, for the months of October, November and December, 1731, No. 421, is contained a Proposal, by Dr. Edmund Halley, for finding the longitude at sea, within a degree or twenty leagues, &c. In the conclusion of this paper, Dr, Halley, in speaking of John Hadley, Esq. VP.R.S, (“to whom,” as he observes, “we are highly obliged for his having perfected and brought into common use the reflecting telescope,”) says—He “has been pleased to communicate his most ingenious instrument for taking the angles by reflection,” (referring, here, to the Philos. Trans. No. 420;) “it is more than probable that the same may be applied to taking angles at sea, with the desired accuracy.”

In Mr. Logan’s account of Mr. Godfrey’s invention, dated June 28, 1734, he says: “Tis now four years since Thomas Godfrey hit on this improvement; for, his account of it, laid before the (Royal) Society last winter, in which he mentioned two years, was wrote in 1732; and in the same year, 1730, after he was satisfied in this, he applied himself to think of the other, viz. the reflecting instrument, by speculums for a help in the case of longitude, though ’tis also useful in taking altitudes: and one of these, as has been abundantly proved by the maker, and those who had it with them, was taken to sea and there used in observing the latitudes the winter of that year, and brought back again to Philadelphia before the end of February 1730–1, and was in my keeping some months immediately after.”

In Mr, Logan’s prior letter to Dr. Halley (dated May 25, 1732,) he says, that about eighteen months before, Godfrey told him, “he had for some time before been thinking of an instrument for taking the distances of stars by reflecting speculums, which he believed might be of service “at sea;” and that, soon after, Godfrey shewed him an instrument, which he had procured to be made, for the purpose. Thus, the time to which Mr. Logan refers Godfrey’s communication of his improvement to him, would make its date to be about the month of November, 1730.

In the Rev. Mr. Vince’s great work, entitled, A Complete System of Astronomy, (and contained in “A Treatise on Practical Astronomy,” at the end of the second volume of that work,) is an entire chapter on “Hadley’s Quadrant;” giving a particular description of the instrument, with rules for the computations from the observations and illustrations of them by examples. In this Treatise, the author says, that the instrument took its name from the “inventor,” John Hadley, Esq. and observes, that not only the science of navigation is greatly indebted, to this “incomparable instrument,” but such are its various uses in astronomy, that it may not improperly be called “a portable observatory.” Mr. Vince further observes, that in the year 1742, about ten years after Mr. Hadley’s invention (for so he styles it) was published, a paper in Sir Issac Newton’s own hand-writing was found among Dr. Halley’s papers, after the Doctor’s death, containing a figure and description of an instrument (referring to Philos. Transactions, No. 465,) not much different in its principle from this of Hadley. He adds, that as Dr. Halley was alive when Mr. Hadley’s instrument was shewn to the Royal Society, and he took no notice of this paper of Sir Isaac Newton, it is probable he did not know there was such an one. In another part of his work (under the head of The History of Astronomy, vol. ii. p. 280.) Mr. Vince asserts, that the first person who formed the idea of making a Quadrant to take angles by reflection, was Robert Hook; and he was born in 1635. On the whole, however, the learned author draws this conclusion:—“Both Sir Isaac Newton and Mr. Hadley therefore seem entitled to this invention.”

Mr. Lalande, speaking of this instrument, says: “Le“Le Quartier de Reflexion, exécuté en 1731 par Hadley, a donné un moyen facile de mesurer les distances sur mer, à une minute pris, aussi bien determiner le lieu de la Lune en mer.” See his Astronomie, vol. iii. p. 654.

From these facts, and a careful examination of the papers themselves, here quoted and referred to, the scientific reader will be enabled to decide upon the true merits of the controversy that has so long subsisted, concerning the respective claims of Godfrey and of Hadley, to the invention of the instrument that bears the name of the latter.

Before this subject is dismissed, however, it will not be deemed improper to add, that the late Dr. John Ewing communicated to the Am. Philosophical Society an account of an Improvement in the construction of (what he terms) “Godfrey’s double reflecting Quadrant,” which he had discovered in the spring or summer of the year 1767: this will be found in the first volume of the Society’s Transactions. In the conclusion of this communication, Dr. Ewing says:—“This improvement of an instrument, which was first invented and constructed by Mr. Godfrey of this city, and which I do not hesitate to call the most useful of all astronomical instruments that the world ever knew, I hope will make it still more serviceable to mankind.”

This communication to the Society by Dr. Ewing, was made in the year 1770. In one concerning the comet of that year, and made by Dr. Rittenhouse about the same time, the instrument to which Dr. Ewing’s improvement applies, is called Hadley’s Quadrant: but perhaps Dr. Rittenhouse so named it, in conformity to common usage.

A36. This I know has been pretended to. But it is easy to make geometrical conclusions come out as we would have them, when the data they are founded on, are so uncertain that we may chuse them as suits our purpose.

A37. This circumstance tends gradually to lessen the variety of the seasons.

A38. This was Tobias Mayer, who was born at Marbach in the principality of Wurtemberg, in the year 1723: he rendered himself celebrated in astronomy, by having calculated the best tables of the moon, and by an excellent catalogue of stars. He died at Gottingen in 1762, at the age of thirty-nine years. W. B.

A39. It may happen that any of the planets, about the time they become stationary, shall describe a loop about some small fixed star, in such manner as might be easily mistaken for the star making part of a revolution about the planet. This I suspected to have been the case with the above observation of Montaigne. But the times set down do not confirm the suspicion.

A40. See page 320 of the foregoing Memoirs.

A41. See page 154 of the foregoing Memoirs.

A42. Mr. T. T. proceeding on a different supposition, has computed twenty-seven billions of years necessary for that purpose.

A43. “The main-wheel, which is fixed on the barrel on which the cat-gut runs.” Mr. Voight.

A44. “A perpetual rochet is a spring lying between the main-wheel, and a plate which is so high in diameter as to be nearly of a height with the bottom of the main-wheel teeth, and is cut with fine teeth all round, in the shape of a fine saw. A click on an axis is fixed between the two frame-plates, with a weak spring that forces this click into the fine saw-teeth, which keeps the plate from moving backwards when the clock is winding up. This fine rochet-wheel is fixed on the barrel-arbour or axis, the same as the main-wheel. The barrel-rochet comes close against the plate of the fine rocket, which has a click screwed on the front, corresponding with the barrel-rochet, and a spring above that rochet’s click, which forces that click into the barrel-rochet’s teeth: it is this that makes the clattering noise, which is heard when a clock is winding up: There is a middling strong spring placed between two arms of the cross of the main-wheel, bent like the space of the two arms between which it acts; and this spring is as broad as the thickness of the cross-arms. One end of that spring is fastened to the inside of the fine rochet-plate: the other end lies on the other cross-arm, and acts on that like a gun-lock mainspring on the cock-tumbler. When the clock or time is set a going, and the maintaining power or weight of the fusee or barrel, this power will raise that spring so far as to resist the maintaining power, and becomes stationary as long as the time-piece is going; and when it is wound up, this spring in the main-wheel cross will expand itself, press on the cross-arm, and force that wheel forward, with nearly the same power as the maintaining power would give: the click for the fine-teethed rochet falls into one of those fine teeth, and keeps that rochet steady, without having the least motion, as long as the winding-up of the clock continues; and by this means a time-piece can lose no time in winding up: hence it is called a perpetual rochet; which requires the most accurate workmanship, in its construction.” Mr. Voight.

A45. This description is drawn up from two separate accounts of the instrument, with which the Writer of these Memoirs was obligingly furnished, in writing, by Robert Patterson and the late David Rittenhouse Waters, Esquires, of Philadelphia. Mr. Patterson mentions, that he recollects his having seen the Hygrometer so described, in Dr. Rittenhouse’s Observatory, about thirty years ago.

A46. The second volume of the Transactions of the American Philosophical Society contains a letter, written on the 13th of November, 1780, by Dr. Benjamin Franklin, then in France, to Mr. Nairne, of London: but it was not communicated to the Society, until January, 1786.

In that letter, Dr. Franklin suggests to Mr. Nairne (an eminent optician, and mathematical instrument maker,) the idea of an Hygrometer made of wood; in preference to metalline instruments, for the purpose of discovering “the different degrees of humidity in the air of different countries;”—an idea which occurred to the Doctor, in consequence of a casual circumstance, mentioned in his letter.

Dr. Franklin supposed “a quick sensibility of the instrument, to be rather a disadvantage” to it; “since,” says he, “to draw the desired conclusions from it, a constant and frequent observation day and night, in each country—when the design is, to discover the different degrees of humidity in the air of different countries—will be necessary for a year or years, and the mean of each different set of observations is to be found and determined.”—“For these reasons,” continues the Doctor, “I apprehend that a substance which, though capable of being distended by moisture and contracted by dryness, is so slow in receiving and parting with its humidity that the frequent changes in the atmosphere affect it sensibly, and which therefore should, gradually, take nearly the medium of all those changes and preserve it constantly, would be the most proper substance, of which to make an Hygrometer:”—and he believes good mahogany wood to be that substance. In the concluding part of this letter, Dr. Franklin says to his correspondent: “I would beg leave to recommend to you—that you would take a number of pieces of the closest and finest grained mahogany that you can meet with; plane them to the thinness of about a line, and the width of about two inches across the grain, and fix each of the pieces in some instrument that you can contrive, which will permit them to contract and dilate, and will shew, in sensible degrees, by a moveable hand upon a marked scale, the otherwise less sensible quantities of such contraction and dilatation.”

Hence it appears, that Franklin and Rittenhouse conceived an idea of the same kind, nearly at the same time: but that the latter carried his invention into practice, three or four years before the theory of the former, founded on similar principles, had been announced to the American public, or, as it is believed, was made known to any other person than Mr. Nairne. W. B.

A47. In a table (in the 2d vol. of Lalande’s Astronomie,) entitled, “Passages de Mercure sur le Soleil, calculés pour trois sièclessiècles par les nouvelles Tables,” the transit of that planet, above referred to, is thus set down by Lalande, at Paris; viz.

Year. Conjunct. Mean Time. Geocentric Long. Mid. Mean Time Semi-dura. Short. dist.

1776. Nov. 2. 9^h10′7″. 7.11°3′36″. 9^h49′53″. 0^h36′42″. 15′43″.A

W. B.

A48. The calculations are here wanting, in Dr. Smith’s MSS.

A49. Here Dr. Rittenhouse’s ends: The remainder of the versification is continued by another hand.

A50. He never professed the business of making watches: the first mechanical occupation he assumed was that of a clock maker, an employment he pursued many years, in the earlier part of his life. W. B.

A51. Having, in the preceding note, adverted to the unimportant error in the text, wherein our Philosopher is stated to have pursued the employment of a watch-maker, instead of that of a clock-maker; it becomes necessary to notice, in this place, another mistake, though likewise an inconsiderable one, into which the liberal and candid writer of the article, above quoted, has been led. Dr. Rittenhouse’s Observatory, at Norriton—the place of his original residence and the seat of his farm-house—was erected prior to the celebrated “Astronomical Observations” made by him, in the year 1769; which were those relating to the Transit of Venus over the Sun’s disk, on the 3d of June in that year. W. B.

A52. The time above referred to, is supposed to have been in the year 1790 or 1791; though perhaps it may have been somewhat earlier. Dr. Sproat died in the autumn of 1793. W. B.

A53. An uncle of Copernicus was Bishop of Warmia, (in Ermeland, a little province of Poland,) and gave him a canonry in his cathedral of Frawenberg, a city in ducal Prussia, situated on the Frische Haff, at the mouth of the Vistula: it was there he began to devote himself to astronomy, at the age of twenty-eight years. His great work, De Revolutionibus Orbium Cœlestium, was completed about the year 1530: but his apprehensions of meeting with persecution from the bigotted ignorance of the age, in consequence of the system he therein promulgated, deterred him from publishing it until thirteen years after that period; and it is supposed that the agitation of his mind, occasioned by its appearance in the world, produced the sudden effusion of blood, which terminated his life on the 24th day of May, in the year 1543. W. B.