was at Ottumwa, describes the corona as approaching much more nearly in regularity the four-rayed form generally given, and which

FIG. 4.

had always seemed idealized or conventional. The S.W. ray was, however, unequally subdivided with the smaller part towards the north. The whole seemed of a fibrous, slightly curled or twisted character, somewhat like a cirrus cloud, and of silvery whiteness. The prominences, especially the large one a little to the left of south, seemed at the first instant of a dazzling white, but after his attention had been diverted for a few moments, it appeared of a brilliant decided rose colour bordering on crimson, and remained of this colour to the close. To Mr. Zentmayer, who was engaged at the camera and had used neither telescope nor screen, it appeared white, with a slightly roseate hue. To Mr. Moelling, under similar conditions, it appeared white throughout. Messrs. Brown and Baker, who had a short glimpse of it from the door of the dark room, rather incline to the opinion that it was white. Professor Pickering, who was at Mount Pleasant, Iowa, describes the corona as an irregular four-pointed star with, of course, a black centre. Two of the rays were nearly vertical and two horizontal, the left-hand one pointing somewhat downward, while between it and the lower ray was a fifth smaller point. The colour was pure white, very different from the full moon, but resembling a cumulus cloud. Its texture resembled the ragged edge of a thundercloud, or the crest of a wave torn by the wind. The striae were not radial but spiral, as if the sun had been turned in such a way that the upper edge moved towards the east.

During the totality Professor Young gave special attention to observation of the corona with the spectroscope. He found that, in place of a subdued solar spectrum, which would have been anticipated from the reports of former observations, it yielded a spectrum of bright lines. These are represented in the coloured illustration, and below the spectrum of the corona is given a copy of the spectrum of an aurora borealis as observed by Professor Winlock on the evening of April 15th. From the close accordance between the coronal lines and three of the auroral lines, Professor Young considers it almost certain that the corona is simply an electric discharge, no doubt varying with great rapidity, as we see in the case of the aurora; in fact, that the solar corona is a permanent aurora. It is, however, right to state that in an article by

Mr. J. N. Lockyer in Nature,' for November 4th, he throws some doubt on this conclusion, and hesitates to regard the question as settled, were the new hypothesis less startling than it is.

The most complete series of spectroscopic observations were those taken of the prominences. During totality nine bright lines were observed by Professor Young in the spectrum of one of the protuberances, viz. o dazzling in brilliancy; 1017.5 (near D, the numbers refer to Kirchhoff's scale) very bright, but not equal to c; 1250 ±20, very faint, position only estimated; 135020, like preceding; 1474 (a little below E), conspicuous, but not more than half as bright as 1017.5; F next to c in brightness; 2602 ± 2, a little fainter than 1474, position determined by micrometrical reference to the next; 2796, a little below G; the well-known н y line in brightness between 1017.5 and 1474; and finally h, or H 8, somewhat brighter than 1474. b it is supposed was not seen; on account of a mistake in carrying that portion of the spectrum through the field, there was no prominence on the slit. The lines marked H in the coloured illustration are hydrogen lines.

The opportunity which was afforded by the total obscuration of the sun's light was taken advantage of to search for planetary bodies between Mercury and the sun, but without success, although Mercury, Venus, Mars, Saturn, Regulus, and Arcturus were plainly visible. The horizon all around was lighted up by a sort of dim twilight for four or five degrees in breadth, and above this rim of light hung a leaden canopy, increasing in depth towards the zenith.

At the Ottumwa station a curious appearance was noticed by Mr. Zentmayer. During the time that the pictures of the partial phase were being taken at long intervals, the ground-glass plate was put in the camera to note any irregularities in the clock movement, should they occur. About twenty-five minutes before the totality, Mr. Zentmayer observed some bright objects on the groundglass, crossing from one cusp to the other of the solar crescent. Each object occupied about two seconds in passing, and they all moved in right lines, nearly parallel, and in the same direction. These points were well defined, and conveyed to the mind of Mr. Zentmayer, who is accustomed to the use of the camera for photographic purposes, the strong impression of being images of objects, and not points of light merely. It is, moreover, certain that the objects, whatever they might be, must (in order to have produced such sharply-defined images on the ground-glass) have been several miles distant from the telescope, as even a point of light at a less distance would have produced an enlarged image, with a hazy

border.

The most complete account of the photographic operations is recorded in the report to Professor Morton by Dr. Mayer, who was the chief of the Burlington party. They arrived at their destination

on August 4th, and up to the morning of the 7th they were occupied in putting together the base and frame of the telescope, mounting the bed-plate, the polar and declination axis and circles, the cradle holding the telescope, fitting-in the tube and optical part, adjusting the verniers and bringing the instrument into altitude and azimuth adjustment. The whole of Friday, August 6th, there was a driving rain, an east wind, and a dull murky atmosphere, foreboding the worst results on the morrow-after having spent previous weeks in preparation, and having travelled over a thousand miles, in the hope of carrying back with them permanent photographic records of the long-thought-of eclipse.

As they retired to rest there appeared signs of the clouds breaking. They had barely fallen asleep when the clerk, according to previous arrangement, woke them with the agreeable news that there were plenty of stars. They were soon dressed, and were charmed by the sight of a cloudless sky; and Professor Coffin, Drs. Gould and Mayer were up all night putting their own special instruments in adjustment. When all was finished, the sun was rising, and the air as pure and serene as one could wish. On Saturday morning the chronograph was mounted, and electric wires were led to the camera, to Professor Young's spectroscope, and to the station of Dr. Gould outside the building. The two threads of the reticule of the camera were placed one parallel and the other at right angles to the celestial equator, and experiments were now begun by Mr. Willard to ascertain the chemical focus. This was obtained after the tube had been following the sun for an hour or more, and after the focus was fixed the clockwork was kept going, so that no change in focus should supervene from a change in temperature in the lenses and tube. The clockwork adjustment had been regulated with such accuracy that it drove the telescope so that a star would remain closely bisected for twenty minutes. By 3 P.M. all was in readiness, and each one at his allotted post of duty, ready for work.

The image of the sun was 2.04 inches in diameter, and was taken on a 4× 5 inch plate. Mr. Zentmayer had so constructed the camera eye-piece, that the image of a reticule of two spiderthreads at right angles to each other was formed on the plate with the image of the sun, and these threads were so mounted that they could be adjusted respectively parallel and at right angles to the celestial equator, and thus fix on the photographs the positions of the sun and moon, and give the position angles of points on the surface and periphery of the sun.

The tube carrying the camera lenses screwed into a plate in which, immediately in front of the anterior lens, was a guide, in which a thin plate having a horizontal slot of 0224 inch in width was caused to descend by the action of a spring. This was used

for the partial phases. During totality the full aperture of the object-glass was employed, and a slide plate was used, having a circular opening which allowed the full beam to pass. This plate had two falls instead of one. On setting the plate free by the top trigger it fell, and the collodion plate was exposed to the entire beam; after the desired exposure a lower trigger was relieved, and the plate made a second fall, and the lens being covered by the top of the plate, the exposure ceased. These triggers were connected with a Morse register having a paper fillet running through it; at every second the clock for an instant opened the electric circuit, and there was a very short break made in the line marked by the pen on the fillet; thus the seconds of time were stepped off in space on the paper ribbon. The triggers were so connected with this chronograph that an additional break was made during the time the photographic plate was being exposed. By measuring this break on the paper ribbon and comparing its length with the length of the second in which it occurs, the exact fraction of the second during which the plate was exposed will be given.

Dr. Mayer arranged for his own duty to keep the telescope in adjustment, and to manipulate the apparatus of exposure and chronographic registration, while Mr. Willard placed the plate in the camera and gave the several times of exposure he desired during totality. Mr. Phillips coated the plates and handed them to Mr. Montford, who carried them to Mr. Willard, and thence, after exposure, to Mr. Mahoney, who developed them, assisted by Mr. Leisenring.

The wall of the dark room adjoining where the telescope stood was fitted with two dark valves, or dumb waiters, by which the plate-holders could be passed in and out without the admission of light or the necessity of any of the operators moving from their places. Seven negative baths were used, standing in a trough of water to keep them cool, four plate-holders, and a large wooden trough with grooved sides, similar to a negative-rack; this was filled with a weak solution of hyposulphite of soda. In the dark room the first operator's duty was to coat plates and put them into the baths; the second took them out, put them into the plate-holders, and passed them out of the room by means of one of the dumb waiters. After exposure, the holders were returned to the dark room by the second dumb waiter, when the third operator took the plate from the holder, developed, washed, and then dropped it into one of the grooves in the large fixing trough. There the plates remained slowly fixing till after the eclipse was over, when they were taken out in the same order in which they were put in, washed, and numbered with a diamond.

At the telescope Mr. Rock was detailed to attend to the very important duty of calling out the seconds of the chronograph-fillet;

Mr. Kendall called out the minutes at each 60-seconds call of Mr. Rock, and wrote it on the fillet. He also had charge of the chronograph, and started it when Dr. Mayer called "clock," while, at the same signal, Mr. Rock began the registration of seconds.

Dr. Mayer had laid out the following programme of work:-First to take in rapid succession, beginning 10 seconds before the computed time of first contact, a series of five photographs. Secondly, one just before second contact, one just after second contact, as many as possible during totality, one just before the end of totality, and another just after the sun reappeared. Thirdly, to take again a series in rapid succession about the end of the eclipse. Fourthly, during partial phase, to take a picture every four or five minutes.

When the chronometer marked 12 h. 48 m., Mr. Rock began to count and register the times on the fillet. Every one was at his post, the lanterns lighted, and nothing could be heard but the count and tap of the chronograph. At 12h. 49 m. 45 s. the first photograph was taken, and following at intervals of from 10 to 12 seconds five perfect pictures were secured. The contact is first visible on the third. Photographs were now leisurely taken at intervals of about four minutes, until twelve plates in all were taken.

About five minutes before totality, Mr. Willard removed the diaphragm of two inches aperture, which was used during partial phase, and exposed the full aperture of the object-glass, whilst Dr. Mayer changed the slide with 0224-inch slot for the one which admitted the whole beam at once on the plate in the camera.

The order was given to prepare the plates. The first plate was taken at 13 h. 51 m. 39.15 s., or 7 seconds before the time of second contact as observed by Professor Coffin. The slide was soon reset for another exposure, and as Mr. Willard desired the first plate of totality to be exposed five seconds, Dr. Mayer kept on counting zero, zero, zero, with the taps of the chronograph, until striking the upper trigger at zero, he counted one, two, three, four, five, when the lower trigger was struck and the plate removed.

Counting the first plate, taken seven seconds before second contact, six photographs were taken in 2 m. 3 s. After the sixth was removed there still remained 50 s. of total phase. There was a delay in the plate. The observer grew impatient; he called plate! plate!! but, alas, it was found impossible to manipulate more than six plates in two minutes and three seconds. The store had been used up too rapidly, and so they did not succeed in getting an impression just before the sun came forth. The next plate was taken 29-2 seconds after third contact, and is a valuable photograph of a thin crescent, with the cusps sharply cut.

Dr. Mayer describes the appearances during totality in the following words:" About 15 minutes before totality it became so cool that I was obliged to put on my coat. A minute or two before