In order to have every chance of success it is necessary to procure a lens of large aperture and the shortest attainable focal length, and to have a grating of the largest size adjusted in such a way as to utilize the beam of light to the best advantage. Moreover, the apparatus must be mounted equatorially and driven by clockwork so that the exposure may last the whole time of totality and the photographic work mus: be done by the most sensitive wet process. After some experiments during the summer of 1877 and the spring of 1878, the following form was adopted.

The lens being of six inches aperture and twenty-one inches focal length, gave an image of the sun less than one-quarter of an inch in diameter and of extreme brilliancy. Before the beam of light from the lens reached a focus it was intercepted by the Rutherfurd grating set at an angle of sixty degrees. This threw the beam on one side and produced there three images-a central one of the Sun and on either side of it a spectrum; these were received on three separate sensitive plates. One of these spectra was dispersed twice as much as the other, that is, gave a photograph twice as long. This last photograph was actually about two inches long in the actinic region. If, now, the light of the corona was from incandescent gas giving bright lines which lay in the actinic region of the spectrum I should have procured ring-shaped images, one ring for each bright line. On the other hand, if the light of the corona arose from incandescent solid or liquid bodies or was reflected light from the Sun I was certain to obtain a long band in my photograph answering to the actinic region of the spectrum. If the light was partly from gas and partly from reflected sunlight a result partly of rings and partly a band would have appeared.

Immediately after the totality was over and on developing the photographs, I found that the spectrum photographs were continuous bands without the least trace of a ring. I was not surprised at this result because during the totality I had the opportunity of studying the corona through a telescope arranged in substantially the same way as the photo-telespectroscope and saw no sign of a ring.

The plain photograph of the corona taken with my large equatorial on this occasion shows that the corona is not arranged centrally with regard to the sun. The great mass of the matter lies in the plane of the ecliptic but not equally distributed. To the eye it extended about a degree and a half from the sun toward the west while it was scarcely a degree in length toward the east. The mass of meteors, if such be the construction of the corona, is therefore probably arranged in an elliptical form round the sun.

For the fortunate results of this expedition we are not a little indebted to the railroad and express companies. The Pennsylvania, the Chicago and Northwestern and the Union Pacific railroads, the Pullman Palace Car Company, and the American and Union Pacific Express Companies made the most liberal arrangements, and Mr. Galbraith, the Superintendent of the Repair Works at Rawlins, gave us the free use of his private house and grounds. Of the citizens of Rawlins it is only necessary to say that we never even put the lock on the door of the Observatory, and not a thing was disturbed or misplaced during our ten days of residence, though we had many visitors. They sent us away with a serenade.

ART. XXV.-Discovery of an Intra-Mercurial Planet; by JAMES C. WATSON.

Ar the recent total eclipse of the sun I was occupied exclusively in a search for any intra-Mercurial planet which might be visible. For this purpose I employed an excellent fourinch refractor, by Alvan Clark & Sons, mounted equatorially, with a magnifying power of forty-five. There were no circles originally attached to the instrument and, accordingly, I placed on it circles of hard wood, the declination circle being five inches and the hour circle four and three-quarter inches in diameter. On these I pasted circles of card-board, and pointers were provided so that I could mark with a sharp pencil the position corresponding to any particular pointing of the instru ment. This method does not compare in accuracy with graduated circles and verniers, but it has the advantage, and a very important one in the present case, of avoiding the uncertainty which might be attributed to erroneous readings of the circles. To read the divided circles would require considerable time, while the pointings can be marked on the paper discs in a few moments. And besides, while a doubt might be raised as to the correctness of the recorded circle readings, no such doubt can exist in reference to the positions marked on these paper circles. The chronometer times corresponding to each pointing were recorded, and the designation of the object observed was also marked on the paper discs, so that there is no difficulty in identifying the several marks.

Before the commencement of the eclipse, the inclination of the polar axis of the instrument was adjusted and it was brought into the meridian as nearly as possible. The error therefore arising from the imperfect adjustment of the equatorial mounting will be small. A few minutes before the totality

of the eclipse I swept over the regions east and west of the sun, from eight degrees to fifteen degrees distant, but no stars were seen. Immediately after the commencement of totality I began sweeps east and west extending about eight degrees from the sun. I had previously committed to memory the relative places of stars near the sun down to the seventh magnitude, and the chart of the region was placed conveniently in front of me for ready reference whenever required. The first sweep began with the sun in the middle of the field, and extended eastward about eight degrees and back, and I saw & Cancri and smaller stars marked on the chart. The next sweep was one field farther south, and eastward and back as before. Then placing the sun in the field I commenced a corresponding sweep to the westward. Between the sun and @ Cancri and south of the middle of the field, I came across a star, estimated at the time to be of the four and a half magnitude, which shone with a ruddy light and certainly had a larger disc than the spurious disc of a star. The focus of the eye-piece had been carefully adjusted beforehand and securely clamped, and the definition was excellent. I proceeded, therefore, to mark its position on the paper circles, and to record the time of observation. It was designated by a. The place of the sun had been recorded a few minutes previously and marked S1. Placing my eye again at the telescope I assured myself that it had not been disturbed, and proceeded with the search. I noticed particularly that the object in question did not present any elongation such as would be probable were it a comet in that position. In the next and final sweep I brought into the field what I supposed to be 【 Cancri, although it appeared very much brighter than what I expected from the appearance of Cancri which I had seen in the first sweep. I proceeded to record its position on the circles with the desig nation b. Before this was completed the total eclipse was over, and I ran across to where Professor Newcomb was observing in hopes of being able to point his larger instrument upon the star a before the light became too bright. I found, however, that he had a suspicious star in the field, and was then engaged in making the circle readings, so that his telescope could not be disturbed. I then went back to my own telescope, but the sunlight was already too intense to enable me to see the star last in the field. I did not therefore determine whether the instrument had been disturbed by a gust of wind from the west which came just before the sun reappeared. The telescope was clamped pretty tight in declination but it had a freer motion in right ascension. It was placed in the lee of a sand ledge and it was, hence, quite well protected from the wind. Sections of snow fence belonging to the railroad had

AM. JOUR. SCI.-THIRD SERIES, VOL. XVI, No. 93.-SEPT., 1878.

also been placed along this ledge as a more complete protection in case of very strong winds.

Upon reading the circles and reducing the observations, it is rendered probable that the telescope was disturbed in this instance; but I give the observations as they were made complete, in order that they may be made available in any future discussion. The places of the sun were again recorded and verified, and thus the position of the star a (which I believe to be an intra-Mercurial planet) can be determined relatively to the sun. The linear distances on the paper discs were roughly measured immediately after the observations, and the result was to show that the object which I had designated by a on the circles is not a known star. Since my return to Ann Arbor, I have placed the paper discs on the axis of a graduated circle, and setting them by means of a pointer, I have read off the positions. They are shown by the following table, in which the readings given are the mean of five readings on each mark:

The three comparisons of (a) with the sun give

The place of the sun for the instant of observation is

It was not possible in the brief period of totality to change the eye-piece in order to observe the object under a high power. I can only state in addition to the above, that the appearance of the object arrested my attention even before I moved the telescope to the known star farther to the eastward. It was

very much larger than this star, which was Cancri, and its light was quite red. The appearance of the disc was such as to lead me to believe that it was situated beyond the sun.

I have not had an opportunity to make any calculations sufficient to determine whether the place observed can be reconciled with the reported observations of spots supposed to have been planets in transit across the sun. This I will do hereafter. The star marked (b), and supposed to be Cancri, was 0° 35′ south from the sun, as determined from the place marked on the paper circle. If the telescope was disturbed by the wind before the pointing was marked, the disturbance would probably be wholly in right ascension, since the motion in declination was pretty nearly clamped. In regard to the star (a), which I consider to be the planet sought, there is no uncertainty whatever, beyond the unavoidable errors of the record as made. I consider the place given to be trustworthy within 5' of arc. It is to be hoped that persons who have made suitable photographs during the totality will examine the plates carefully in the region indicated. It is possible that the planet may appear upon some of them.

My station for observation was at Separation, Wyoming Territory, on the Union Pacific Railroad. It is near the summit of the Rocky Mountains, in a circular walled plain of several miles diameter, at an elevation of about 7,200 feet above the level of the sea. It is proper to add further, that the major part of the expenses of my expedition were defrayed by the U. S. Naval Observatory from the appropriation made by Congress for the observation of the eclipse.

Ann Arbor, August 13, 1878.

ART. XXVI.—New Pterodactyl from the Jurassic of the Rocky Mountains; by Professor O. C. MARSH.

THE Pterosaurian remains hitherto discovered in this country are all from the Cretaceous, and most of them belonged to animals of gigantic size. So far as known, they were all destitute of teeth, and hence belong to the order Pteranodontia. A characteristic specimen recently found in the Upper Jurassic of Wyoming, and now in the Yale College Museum, is the first indication of this group of reptiles from this formation in America. The specimen, which is in good preservation, is the distal portion of the right wing metacarpal, and indicates a small pterodactyl having a spread of wings of four or five feet. The shaft of this bone at its upper portion is oval in transverse section, but near the condyle it is sub-trihedral, with a distinct