Part 2 — THE TOTAL ECLIPSE OF AUGUST SEVENTH.

The recent solar discoveries, of which mention has been made in past numbers of this magazine, have on the whole increased the interest attached to the observation of eclipses, though in some respects the importance of these phenomena as opportunities of extending our knowledge of the constitution of the sun has been diminished. It will be remembered that immediately after the total eclipse of last year in India, it was found that the great prominences on the rim of the sun which are never seen with any ordinary appliances, except on these occasions, could be observed at any time with the spectroscope, and that by means of this admirable instrument their shape as well as the spectral lines indicating their chemical composition could be determined; and since that time many observations of them have been made, and interesting conclusions arrived at on both these points, as stated in the article translated in the last number. The principal ones as yet established with certainty are, that they are gaseous, and mainly composed of hydrogen, and that they change their shape with astonishing rapidity, some of their particles perhaps moving with the inconceivable velocity of one hundred miles a second. At any rate, immensely energetic forces and rapid movements must be required to change essentially the shape and position of these masses—which often have ten times the diameter, or a thousand times the volume of the earth—in a quarter of an hour.

So we are not now obliged to wait a year or more and travel several thousand miles to observe for a few minutes these peculiar and still somewhat mysterious bodies; still, it does not follow that they cannot be better examined at the time of an eclipse, or that new appearances may not be noticed on such occasions, now that we are accustomed to these, from which the other more startling phenomena for a long time diverted attention. Success has excited hope of yet greater successes; and eclipses, though affording but a short time for actual observation, are undoubtedly the best occasions for the observer to learn in what direction his labors should be turned. There are also other things, such as the corona, Baily's beads, possible new planets inside of the orbit of Mercury, etc., which can only be seen at these times.

The eclipse of this year, therefore, was by no means neglected by the scientific men of the United States; in fact, it was felt that the reputation of the country depended upon the skill shown in preparing for and in observing it, and a large number of parties were formed, to be stationed at various points of the path of the moon's shadow or line of totality, so that if clouds should prevent success at one place, it might be obtained at another.

The first point touched by the shadow proper, and at which consequently a total eclipse occurred, was in longitude 165° west from Washington, latitude 53° north, being in Siberia; the last, in longitude 10° east, latitude 31° north, being off the coast of North Carolina. At the former the sun rose totally obscured at half-past four, at the latter it set in that condition, at a quarter to seven; and at the intermediate points the eclipse took place at all the intermediate hours of the day. It is rather singular that, owing to the necessary skip of a day in going round the world, it was Sunday morning in Siberia, but Saturday afternoon in the United States; so that the eclipse may be said to have been one of the longest on record. Its actual duration was, however quite short, half-past four A.M. in Siberia, and a quarter to seven P.M. at the ending point, being about four and half-past six P.M. respectively in New York; giving an interval of two and a half hours in which the shadow passed over the long line connecting these points, which it will be perceived are nearly opposite in longitude.

If it had travelled by the shortest route, it would have passed within three degrees of the north pole, and the eclipse would have been invisible in this country; but, fortunately, it lengthened its course, reaching its highest latitude near Behring's Straits, which it crossed, and then swept to the south-east, crossing the territories of Montana and Dakota, and the States of Minnesota, Iowa, Illinois, Indiana, Kentucky, Tennessee, Virginia, and North Carolina. It could hardly have taken a better route for us.

The length of the line was over seven thousand miles, and the consequent average velocity in passing over it about fifty miles a minute, though in the United States it exceeded that amount considerably. The breadth of the belt traversed was somewhat variable; in this country it was about one hundred and fifty miles. Of course, the sun was partially hidden by the moon over a very large portion of the globe; but the region from which its light was at any time completely excluded was comparatively quite small.

Observers stationed themselves at numerous points, even as far west as Alaska and Siberia; but of course most chose positions within the United States. The writer was connected with a party which was established at Shelbyville, Kentucky.

The general diffusion of intelligence, both subjective and objective, as we may say, had of course excited great interest in the eclipse among the people, especially in that part of the country actually within or bordering upon the limits of totality; and though, of course, the nature of the expected event was fully understood by all the educated portion of the community, and by many of the uneducated, still there were some, especially in the rural districts, who vaguely apprehended some great event, to be probably of a disastrous nature, (a hailstorm was the most popular;) and perhaps were as much terrified in anticipation as any entirely ignorant people have ever been at the actual occurrence of this most impressive and sublime spectacle.

Of course, excursions were planned by railroad companies and others to points on the line of the shadow, the usual directions for observing were extensively circulated, and the eclipse was made the catch-word for many advertisements whose substance had no connection with it. We are afraid that many persons may have lost the most beautiful features of the scene by a too persistent use of smoked glass, which of course was not necessary during or even near the time of the total obscuration.

The weather for some days previous was not very promising—not on account of too much rain, but owing to the absence of it; and every evening the sun set in a bank of haze, which each day seemed to increase, and no storm occurred to clear the air of the burden accumulated by the drought. This was particularly unpromising for the photographers, who needed really clear air for good work; the times of beginning and ending, to which, formerly, great importance was attached, could probably have been observed nearly or quite as well through haze, or even thin cloud.

We have just implied that less consequence is now attached to the time observations than was formerly the case; this is due to the great perfection which the lunar and solar theories have now attained, which is such that the prediction of the positions of the sun and moon, and even of the beginning and ending of an eclipse, can be made with greater accuracy, perhaps, than almost any one observer could note them. Still, by combination of all the results, some slight corrections to the tables now used may perhaps be deduced, and on the present occasion this portion of the work was not disregarded, but provided for with all the appliances of modern science.

The recording of time is now usually made by the electric method, which may be here described briefly, though many are probably familiar with it. The principle is the following, subject to various modifications in the particular form of apparatus: A line is described by a pen made to move uniformly over the paper by means of clock-work. That this line may be indefinitely prolonged without retracing, it is usual to make it a spiral round a horizontal cylinder, which revolves, say, once a minute, while the marking-pen (otherwise stationary) moves slowly from one end of the cylinder to the other, perhaps requiring several hours for the complete passage.

The pen making this line is held in its place by the action of an electro-magnet pulling against a spring; the circuit through this magnet is broken every second by the escapement of a clock or chronometer; the magnet then for an instant ceases to act, and the spring pulls the pen aside, making a break in the line at regular intervals corresponding to every second of time. The same interruption of the circuit can also be made by an observer provided with a key like those used by telegraph operators, and the time of his observation thus registered on the chronograph, as the instrument is called. For identification of the clock-mark preceding his observation, mechanical arrangements can easily be devised, by which the first second in each minute shall be omitted, the circuit not being broken; so that it will be known what second of every minute each mark corresponds to; and the fraction of the second elapsed from this clock-mark to his own can easily be estimated by the eye, or measured more carefully. The reading of the record is, of course, facilitated by having the cylinder revolve once a minute, so that all the clock-marks answering to any particular second (as the twenty-third, for example, of each minute) will come in the same horizontal row; and the marks are not made on the cylinder itself, but on a sheet of paper fastened round it, which can be detached when filled.

Instruments of this character were used at Shelbyville, and also at the border stations near the edge of the path of the shadow, but inside of it, one of which was at Falmouth, about thirty miles south of Cincinnati, the other at Oakland, near the Mammoth Cave. The observations of time were especially important at these places, since, as will readily be seen, the length of time required for a circular or elliptical shadow to pass a point near its edge will vary very rapidly for a slight change in the size of the shadow, or a slight shifting of its path toward or from the point selected. Even rough observations, merely of the duration of the eclipse, made at two such stations on opposite sides of the central line, suffice to determine with great accuracy the dimensions and precise track of the shadow, and thus give the elements of the moon's motion.

We have just spoken of the shadow as being elliptical; this was of course the case, the sun being quite low at the time, so that the round cone of darkness, technically known as the umbra, was cut very obliquely at the earth's surface. To realize the amount of this ellipticity or distortion, one would only need to hold some spherical body so as to cast a shadow on the ground about an hour and a half before sunset. The elongation was also continually increasing as the sun sunk toward the horizon, and its direction changed as the sun at the same time changed its direction or bearing, the longer axis of the ellipse always pointing toward the sun. This axis was, in Kentucky, about three hundred miles long; the shorter ninety; and this elliptical patch of darkness was moving in a course some thirty degrees south of east, or about twenty-three degrees south of its own longer diameter; its speed was about seventy-five miles a minute, or more than the average on the whole track, as before stated, and it required rather less than three minutes to pass any given point on the central line; this was consequently the duration of the totality; and short enough it certainly was, for the amount of work which was to be done by the observers.

For the stations on or near the central line, it was important to obtain the absolute times of the contacts, and for this purpose transits were observed, to get the error and rate of the chronometer, for some time before and after the eclipse. The border observations locate the path on which the shadow travels, and determine its breadth; but to obtain the position of the shadow on this path at any fixed time, the true times of its arrival and departure at fixed points must be observed. But on the border no such preparations were necessary, only the interval being required; and a simple pendulum, without clock-work, was set up for this purpose, which broke the circuit at each second, and thus left its record, serving to count the number of seconds and the fraction between the beginning and end of the totality, which were observed and similarly recorded by means of a break-circuit key. This pendulum was so arranged as to break the circuit on the main telegraph line, and thus to be heard, and record its beats at a number of stations in different towns; but the main circuit did not itself mark upon the registers used by the observers, but mechanically (by means of what is called a relay magnet) broke short circuits set up at their stations, which could also be broken in another place by their own keys, without, of course, interfering with the main circuit itself; so that every observer could receive the pendulum beats upon his own record, without receiving those made by observers at other stations.

On Thursday afternoon, the 5th of August, some showers occurred, but not sufficient, according to ordinary experience, to have much effect in clearing the atmosphere; and on Friday morning the sky became overcast with mackerel clouds of a most unpromising character. All the preparations were, however, hopefully continued, and the photographer, Mr. Whipple, of Boston, took on that day some very successful views of Shelbyville, of the college buildings, and of the party of observers. The principal station had been established in the grounds of the college, the instruments being protected by a large tent; close by was the Coast Survey station, where the chronographs just described for recording time, as well as a transit instrument for observing it, had been placed.

Friday evening was cloudy at Shelbyville, but without rain, and the chance seemed to be gradually diminishing of any thing like a good observation of the eclipse.

The plans for photographing the successive phases were most perfect. The movement of the sun from east to west of course made it necessary that the plate should also move correspondingly, but this was readily accomplished by connecting it with a telescope mounted on an axis parallel to the earth's equator, which axis is itself fixed to another at right angles to it, or parallel to that of the earth; this second axis being turned by clock-work once in twenty-four hours in a direction opposite to that of the earth's rotation, all the parts of the instrument evidently follow the movement of the heavens or of any celestial object to which the telescope may be directed. The axis around which the telescope turns can be rotated by hand or clamped in position, and in connection with the other, which can be disengaged from the clock-work, enables the instrument to be pointed in any direction at pleasure. This style of mounting is known as the equatorial, and is almost always used for astronomical telescopes. It is similar to the ordinary tripod used for small instruments, except in the addition of clock-work, and in having the principal axis inclined toward the pole-star instead of being vertical.

But it was necessary not only to take photographs, but to know the time at which they were taken, that they might accurately measure the movement of the lunar disc over that of the sun. This might have been secured by simply noting them from the face of the chronometer; but the object was more neatly and certainly attained by having the slide itself, as it dropped at the end of the exposure, break the electric circuit, and record its own time on the chronograph.

The spectroscopic work was the most difficult and important of all. Professor Winlock, the director of Harvard College Observatory and chief of the party, had charge of this. Though, as above stated, it has been found that the prominences can be seen with the spectroscope at any time, still the probability that they could be better observed at the time of the eclipse than at other times made it a duty to try the experiment, and the result has, as will soon be seen, proved that such is the case. Another observation was obtained with a spectroscope at Bardstown.

A large number of persons had come in, some from considerable distances, to observe the expected phenomenon. Among them was Mr. Frankenstein, of Springfield, Ohio, an artist, who hoped to paint the appearance of the eclipse and its effect on the landscape. This seemed an admirable idea, and it is quite remarkable that attempts of this kind have not been previously made; as they have not, at least to our knowledge. The circumstances of the present one made it eminently suitable for pictorial effect, owing to the small altitude of the sun; and the landscape, seen from the point selected, (some high hills east of the town,) is certainly one of great beauty.

The clouds broke away at about midnight and the thermometer fell considerably, reading about 59 at sunrise. The observing party improved the opportunity for final adjustments of instruments and preparatory observations, and hope revived in the hearts of all.

The sun rose unobscured on the morning of the 7th, and the day was cloudless till about ten o'clock, when some small cumuli drifted for about an hour across the sky, which then resumed its unbroken blue. The weather was also delightfully cool with a light breeze, which increased in the afternoon, and at four was blowing quite freshly. There were no signs of the predicted hailstorm, and strong faith would certainly have been needed for one to retain a belief of its arrival.

As the prospect of fine weather improved, and in fact seemed almost certain, the people, citizens and strangers, assembled on the observatory hill, and a rope was drawn round the tent where the instruments were mounted, to prevent a natural but dangerous curiosity on the part of those not immediately engaged in the special observations.

Every one now felt that they would be fully repaid for the time and labor devoted to the journey.

At about half-past four the edge of the sun was visibly indented; some persons maintained that they could see the moon some time previous to the contact; but this must probably be ascribed to a lively imagination. Smoked glass now came into demand, and all eyes were anxiously watching the rapidly decreasing orb. I had secured, through the kindness of an influential friend, an excellent position on the court-house, itself a high building and situated on the highest point in the town, commanding a fine view in all directions, particularly toward the north-west, from which quarter the shadow was sweeping toward us at the rate of more than a mile every second.

Some five or six gentlemen had followed me to the roof of the building, after which the ladder leading to the cupola was drawn up, to prevent a general ascent by the crowd below. At a quarter or twenty minutes past five, the wind began to abate, and the darkness was quite noticeable, and of course from that time continually increased, the general effect being like that of moonlight some time before the totality. The darkness was much more striking than at any time during the annular eclipse of 1854; this was probably owing to the total absence of any cloud, which would have reflected and multiplied the light of the unobscured portion of the sun, as on that occasion.

A minute or so before the totality, the complete circle of the moon was easily visible, with faint brushes of light streaming from it in all directions, which were soon to assume much larger dimensions, and, apparently, though not really, a greater brilliancy.

I cast now my eyes to the north-western horizon, and saw a brick-red tinge on the sky evidently caused by the rapidly approaching umbra. The long-expected moment had come; the last direct beam from the sun vanished, and a magnificent corona of rays, faint, of course, compared with the solar light, but bright in the prevailing gloom, shot out round the disc of the moon. These rays were prolonged in four directions at right angles to each other much more than elsewhere; having in these directions a length about equal to the sun's diameter, making the corona or aureola obviously cruciform in its shape.

Venus and Mercury appeared conspicuously on opposite sides of the moon, and Regulus could be seen, though with some difficulty. Several other first magnitude stars appeared in other parts of the sky, Arcturus, Vega, and Saturn being specially noticed by the observers at my side; and undoubtedly fainter ones could have been easily discerned, could one have been willing to divert his eyes from the beautiful sight placed before them, which seemed to surpass the expectations of every beholder. To all our party, I think, it conveyed little or no idea of horror or dread, but only of inexpressible beauty. The moon was at about one sixth of the distance to the zenith above the horizon, so that no straining of necks was necessary to look at it, as it hung over the darkened landscape. Certainly, as it so hung or floated, surrounded by the irrepressible splendor of the great source of light which lay behind it, and attended by its two bright planetary companions, one on each side, it was no unfit type of the glorious mystery which the church had just commemorated on the preceding day. The darkness was not so great as that of moonlight, but of course of a somewhat different character, the light not coming from one definite direction. I think it probable that no shadows were cast, but was too much occupied in other observations to be sure of this point. The birds around the building flew about wildly; and it was said that the fowls went to roost, and the cows started for home, and that the cocks crowed on the reappearance of the sun.

The eclipse had not lasted many seconds when I saw, without specially looking for it, a bright light red or orange drop on the lower edge of the moon, which of course was one of the famous protuberances. It was easily seen with the naked eye, though probably many who had not heard of these appearances did not notice it. Before the end of the obscuration, another appeared on the right where the sun was about to emerge. A third was also visible to the telescope above. Possibly they may have had some connection with the long rays of the corona.

Before we had fairly begun to satisfy our curiosity, a well-marked boundary between the general darkness and a bright portion of sky to the north-west gave warning of the end of the eclipse, and immediately afterward the sun flashed out on the right.

The separation of the discs of the sun and moon during the following hour was probably carefully observed by few except the astronomers and photographers; the moment of interest had passed, and few cared to do more than exchange congratulations on the success of the display. I forgot to notice whether the corona and prominences were visible after the totality; the latter were still seen, according to accounts received from elsewhere, and I met with one gentleman some days afterward who had seen the great protuberance on the lower edge of the sun at Shelbyville, Indiana, a point some fifteen miles from the outside line of totality; he had, of course, no previous suspicion of its existence.

The eclipse was naturally the principal topic of conversation during the evening, and every one was anxious to report his own observations and learn those of others. I found that eleven spectral lines had been seen by Professor Winlock in the great prominence, some of them characteristic of the metal magnesium. He saw only three before and after totality; thus confirming the idea previously entertained, that solar eclipses, though not the only occasions on which these interesting objects may be seen, are, with our present apparatus, far the best. The photographers had taken some eighty pictures, several during the totality, and the times of beginning and ending had been accurately observed both at Shelbyville and, as we afterward learned, also at the stations on the border line, Falmouth and Oakland; which border observations give the position and breadth of the path of the shadow within some eight or ten rods; the southern edge can even be determined with much greater accuracy, owing to a fortunate selection of the station, which proved to be extremely near it. The precise amounts by which these results differ from the previous computations have yet to be determined; but it is probable that the corrections to the tables now used will be very small.

An ingenious method of observing the time of the external contacts, or beginning and end of the whole eclipse, was, as I heard, devised by a gentleman at another station. These phenomena, especially the first, are very difficult to observe accurately, owing to the invisibility of the moon when off of the sun's disc, and the waviness of the sun's limb, making it doubtful that an indentation has been made in it till it has become quite deep, which is, of course, some time after the actual meeting of the two bodies. He observed it with the spectroscope by noting the time of disappearance of one of the lines only visible on the extreme edge of the sun's disc.

Every one not engrossed in some special work had, of course, seen the planets Venus and Mercury; and many had seen others of the first magnitude. The darkness was not so great as was hoped for by those who were searching for intra-Mercurial planets; no candle was necessary for examining the charts which had been prepared. One observer at Shelbyville reported having seen a star of the third magnitude with the naked eye, and as he had no previous knowledge of the existence of such a star in the place in which he was looking, the fact seems indubitable. Dr. B. A. Gould, of Cambridge, who observed at Burlington, Iowa, has since informed me that he saw a star of the fifth magnitude, with a telescope of five inches aperture, near the sun; the star is a well-known one, and the observation shows that, had any planets of that brilliancy (about one fiftieth of that of Mercury) been within three degrees of the sun, within which limits he was restricted in his search by the shortness of time, he would not have failed to detect them.

"Baily's beads" do not appear to have been considered as extraordinary by any of the observers. The limb of the sun just before the totality was of course more or less broken up by the irregularities of that of the moon; but the fragments had no remarkable appearance; and this phenomenon, which has been the subject of so much discussion, seems probably due to irradiation and the difficulty of determining the precise shape of small and brilliant objects.

An able astronomer, who was the chief of the party at Oakland, and who owing to his station being very near the southern edge of the shadow, saw them for fifteen or twenty seconds, says that they presented most clearly the phenomena which he should expect to be caused by the irregular contour of the moon, when its indentations were exaggerated by irradiation.

No discoveries of equal importance with M. Janssen's last year have yet been reported; but as no eclipse has ever been so thoroughly observed, the results cannot fail, when thoroughly collected and compared, to be of great scientific value.