Popular Science Monthly/Volume 3/May 1873/The Sherman Astronomical Expedition
|THE SHERMAN ASTRONOMICAL EXPEDITION.|
SCIENTIFIC observers have long seen the importance of securing a position elevated above the fogs and impurities of the atmosphere at the sea-level, for the purpose of making more accurate astronomical and meteorological observations. Accordingly, Prof. Peirce, the Superintendent of the Coast Survey, petitioned Congress for means to carry out such an undertaking. Congress made an appropriation of $2,000 for this special object, independent of the geographical and topographical constants of the station.
Sherman, in Wyoming, situated on the highest point of the Union Pacific Railway, and on the Rocky Mountain range, was agreed upon as an eligible and convenient locality for the scene of operations; and the months of June, July, and August, 1872, were devoted to the work.
The party consisted of General R. D. Cutts, an experienced officer of the Coast Survey, who had charge of the expedition, Assistant Mosman, Aid Colonna, Prof. Young, Prof. Emerson, and Mr. Mead, of Dartmouth College. There were also a photographer, a mechanician, and two servants. The party had, as an escort, about a dozen soldiers from Fort Russell, at Cheyenne, who assisted in keeping the hourly series of meteorological observations, and were detailed to serve as a protection from possible attacks of hostile Indians.
It was not until July that the members from Dartmouth College were able to join the expedition. The trustees of the college had loaned their valuable telescope for the occasion. It has an aperture of 9 4/10 inches, and a focal length of 12 feet, with clock-work, and the usual accompaniments, and is fitted with an automatic spectroscope, having a dispersive power of 13 prisms. This telescope is one of the best in the county in optical perfection, and in convenience and handiness of mounting.
The summit of a slight elevation was chosen as an eligible locality for occupation. It was a short distance from the railroad-station, and about 40 or 50 feet above the track. Three shanties of rough boards were erected as observatories, one for the transit instrument, one for the meteorological apparatus, and one for the equatorial telescope. The altitude of the observatory is 8,300 feet above the level of the sea, the latitude a little more than 44°, and the longitude about 28° west from Washington.
It was thought that Sherman combined unusual facilities for accomplishing the desired object of the expedition, which was to test the advantages of a great elevation upon astronomic, and especially spectroscopic, work. The currents, impurities, and reflective power of the atmosphere at the sea-level, interfere greatly with studies of this kind, while an elevation of 8,000 feet leaves more than a fourth of the atmosphere below it. The situation was one of remarkable natural beauty. On the east there was little to mark the altitude except the rocky soil and scanty vegetation; on the north there were picturesque piles of granite; on the north-west lay the Laramie Hills; from the northwest to the south towered the mountain-peaks, many of them covered with perpetual snow. Long's Peak and Gray's Peak were 60 miles away at the south; the great mass of Medicine Bow lay at the west, and between them, over the lower ridges, rose some of the high mountains of the Colorado parks.
The party being located, and all arrangements for observation being made as systematic as possible, work was carried on during the summer months in earnest, and attended with valuable results for the initiatory movement of a work of such magnitude. The weather proved to be unusually unfavorable. An old trapper, who had lived among the mountains for twenty years, said that the amount of cloudy and rainy weather was uncommon for the season. With the exception of a week, when every night and a greater part of ever day were fine, clear nights were rare, and clear days less so. There were but two afternoons when work upon the sun could be kept up from noon till sunset, though there were more than twenty cloudless mornings during the same time. The enormous snow-fall of the preceding winter accounted for the unusual weather-condition of the locality, and the snow, in the middle of July, was still lying to the depths of eight feet on the plateau at the base of the Medicine Bow Mount.
Notwithstanding these drawbacks, valuable scientific results were obtained in five different departments of observation, geographical, meteorological, telescopic, spectroscopic, and magnetic.
The geographical position of the station was completely determined, its longitude being obtained by telegraphic communication with Salt Lake City. It will, therefore, be for the future a reference-point and base for the numerous surveys which are being made in that part of the country.
A complete hourly meteorological record was obtained for nearly the whole of the months of June, July, and August, which, from the important position of the station, cannot fail to be of great interest and value.
The telescopic observations were full of promise for the result of future and more thorough work in that department. When the sky was unclouded the atmosphere possessed the most ethereal transparency. At night, myriads of stars invisible at lower elevations were plainly discernible. Nearly all the seventh-magnitude stars of the British Association Catalogue were clearly visible to the naked eye. Prof. Young, to whose report we are indebted for the facts recorded in this article, says that, in the quadrilateral forming the bowl of the "Dipper," he could see distinctly nine stars, with glimpses of one or two more, while at Hanover he could only perceive the three brightest of them. The power of the telescope was correspondingly increased, so that an instrument of 9-4/10 inches of aperture was as effective as one with 12 inches at the sea-level. Some views of Saturn were exquisitely beautiful. The inner satellites, the details and markings of the rings, especially a dark stripe upon the outer ring, were clearly seen under powers ranging from 500 to 1,200. Besides the increase of the range of the instrument, the air was vastly more steady, and faint objects much more clearly defined.
The advantage was still greater in the careful spectroscopic observations that were made. Prof. Young had drawn up at Hanover a catalogue of 103 bright lines in the spectrum of the chromosphere; at Sherman the number was extended to 273, while, at moments of unusual solar disturbance, there were glimpses of at least as many more. Sulphur, strontium, and cerium, are almost certainly proved to be constituents of the solar atmosphere, and zinc, erbium, and didymium are strongly indicated. It was hoped that at the base of the chromosphere there might be seen the reversal of the dark lines of the spectrum, which is so wondrously beautiful at the commencement and close of a total solar eclipse. But in this hope the observers were disappointed; the appearance, at the distance of 1" or 15" from the edge of the photosphere, giving a spectrum principally continuous, most of the. dark lines vanishing or being much weakened. This result confirms the observations of Secchi, who reports at the edge of the sun a layer giving a continuous spectrum.
Curious observations were made upon the spectra of sun-spots, and a catalogue was made of 155 lines more or less affected, either greatly widened or weakened, or reversed. A number of bright lines were found in the spectrum of the nucleus, and some peculiarly shaded, as if they were the product of a combination of elements which, from the reduced temperature over the spots, had been able to exercise their chemical affinities.
Many solar eruptions were watched moving with velocities varying from 150 to 250 miles per second, and pouring forth their whirlwinds and torrents of ejected gas through the molten atmosphere. The most interesting eruption was visible on the surface of the sun itself in the vicinity of a large spot.
The magnetic observations were as satisfactory as any that were made, and yet prove that, although our greatest magnetic storms are only remotely connected with solar influence, every solar paroxysm has a direct and immediate effect upon terrestrial magnetism. On the 3d and 5th of August there were violent paroxysms of solar eruption. At just the minute these eruptions took place, the record of the vertical Magnetic Force shows marked and sudden magnetic impulses, a peculiar shuddering of the magnetic needle for that very time. The photographic copies of the vertical Force Curve at Greenwich and Stonyhurst show marked and characteristic disturbances at the corresponding points, which, allowing for the difference in longitude, were the very moments of time when the solar disturbances were watched at Sherman.
The work of the last summer accomplished by the Sherman Astronomical Expedition points clearly to the inference that a great national observatory should be established without loss of time, in that position on the American Continent most favorable to astronomical observation. Sherman is evidently not the place, on account of weather-conditions, but some mountain-station must be found adapted for the purpose, far above the fogs and impurities of the sea-level. A telescope, the best and largest that scientific resources can furnish, and a corps of observers devoted to the work, must be established on this permanent locality. Then, from this high point, sun, planets, stars, nebulae, comets, and meteors, may be attacked by observers armed with the most effectual scientific weapons, until from the depths of infinite space come answers to some of the great problems that are puzzling the brains of thoughtful students of celestial mysteries.
A recent writer proposes that the whole civilized world shall contribute for a telescope which shall cost 81,000,000. Why should not America contribute enough from her vast resources to possess the most powerful one that can be built, and be the first among the nations to bring about great results, and make certainties of what seem now the shadowy possibilities of the future?