Feb, 2 2, 1877] 



NATURE 



355 



and Wahsatch range, I thought it desirable to carry a telescope, 

 with a view of ascertaining whether there would be sufficient 

 inducement to return with my 12-inch achromatic or 28-inch 

 reflector, and make a prol; nged stay. 



As it was not feasible to take an instrument of any great size, 

 1 contented myself with a small achromatic of unusual excel- 

 lence. Though of only i^ inches aperture, it bears a power of 

 60 completely, and I think would carry lOO. It was provided 

 with a short brass tripod, holdmg an altitude and azimuth move- 

 ment, giving both steadiness and smoothness of acti(m. The 

 eyepiece was capable of adjustment by a rack and pinion, and 

 the object-glass was so arranged in its cell as to be free from in- 

 jurious compression. This little lens stands the severe tests 

 invented Ly Foucault, and in spite of its size is capable of doing 

 good work. 



In such observations on the atmosphere as those proposed 

 during this trip, it is obvious that there are mainly two points to 

 be considered : (i) freedom from tremor, and (2) transparency. 

 A station combining both is most desirable, but a marked pre- 

 dominance of steadiness gives special advantages for celestial 

 photography, while increase of transparency, even if accom- 

 panied by unsteadiness, is of value in eye observations. I had 

 been led to suppose from conversations with Government officers 

 and persons connected with the .'ecological and geographical 

 surveys of the territories, that the Wahsatch range, which is in- 

 termediate between the Sierra Nevada on the west and the true 

 Rocky Mountains on the east, would offer the greatest advan- 

 tages. This supposition turned out to be altogether incorrect, 

 though it might have been aigued that a high range flanked at a 

 distance on either side by other higher ranges should have given 

 the maximum chance for cloudless and still skies. 



We first went to Salt Lake City, which, according to the 

 Casella aneroid I carried, is at an elevation of 4,650 feet above 

 the sea. It lies at the foot of the Wahsatch range. At eleven 

 o'clock on the evening of arrival, August 25, I took some obser- 

 vations from the hotel after carefully centring the object-glass. 

 Saturn looked about the same as on an ordinary night at my 

 observatory. Capella, which was just clear of the house-tops 

 across the street, twinkled as badly both to the naked eye and in 

 the telescope as I have ever seen it at the sea-level. Lieut. 

 Warren, of Camp Douglas [a military post near the city] said 

 there had been a heavy rain the week previous, and the air was 

 more moist than usual. The sun set among just such a bank of 

 clouds as we r.re accustomed to see in New York. I was 

 somewhat prepared for a tremulous condition in these high 

 regions, because, the preceding night, having stopped for a few 

 nights at Fort Steele, on the Union Pacific Railroad, I perceived 

 that Antares twinkled very much, though we were nearly 7,cxx) 

 feet above the sea. 



However, in order to make a thorough trial it seemed best to 

 ascend one of the high peaks of the Wahsatch, and accordingly 

 the Red Butte was selected. The peak proved to be 7,350 feet 

 high. Though it was quite clear wken we started, clouds 

 gathered in every direction as the sun went down, and at night- 

 fall the sky was entirely overcast. Moreover, the wind blew so 

 strongly that it was necessary to retire over the brow of the 

 mountain, and eventually we returned to Camp Douglas. At 

 this point, 5,250 feet above the sea, and about 600 feet higher 

 than Salt Lake City, the telescope was set up to take advantage 

 of some breaks in the clouds, through which the moon, Antares, 

 ^ Ursse Majoris, and Jupiter appeared. With a power of only 

 twenty the twinkling was surprisingly great ; I do not remember 

 ever to have seen it worse with my large instruments. 



These results led to an examination into the meteorology of 

 Salt Lake City, so as to fnid out the rainfall and its distribution 

 and the percentage of cloudy days. 



It appears that the average annual rainfall for the past five 

 years is iSj^"^ inches. There is no p< rfectly dry month, the 

 nearest approach being during the summer. The cloudy dry 

 days are 194 per annum, the disposition being similar to the 

 riinfall. 



A former pupil of mine, and graduate of the University, Dr. 

 Benedict, informed me the Mormons believed the rainfall had 

 much increased since their ct^mmunity had settled in Utah, and 

 'his seems to be borne out by the statement that whereas 

 formerly three gallons of Salt Lake water produced on evapora- 

 tion one gallon of salt, it now takes four gallons to produce the 

 same quantity. 



For these reasons it is doubtful whether there would be enough 

 advantage in bringing a large telescope to this region to make it 

 worth while to encounter the labour and expense. 



On August 30, havinef taken an escort, we moved south from 

 Fort Steele, latitude 41° 48', longitude 107° 09', alont; the North 

 fork of the Platte River, into the main range of the Rocky 

 Mountains. During the fifteen days' expedition there were only 

 two nights on which we saw clouds enough to prevent astro- 

 nomical working, and only one thunderstorm of any moment 

 took place in our immediate vicinity ; about one quarter of an 

 inch of rain fell. The sky was rarely perfectly free from clouds, 

 and many local thunderstorms occurred about the higher peaks, 

 but they seldom extended to the plateaus below. 



September i and 2 our camp was 8,900 feet above the sea ia 

 the vicinity of mountains rising 10,000 and 11,000 feet. These 

 peaks seemed to be nearer than they really were, for the tran- 

 sparency of the air causes estimates of distance to be deceptive. 

 From the top of one I subsequently saw the Seminole Mountain, 

 which was 150 miles distant ; it did not appear to be fifty miles 

 away. The night of September i was quite clear, with very little 

 cloud, and the atmosphere remarkably tranquil. Antares, when 

 near setting, hardly twinkled at all, and Arcturus in the telescope, 

 exhibited lour diffraction rings unbroken by flickering. The 

 central disc was as hard and sharply defined as the pin-hole in 

 the lamp-screen I am accustomed to use in testing specula and 

 lenses. I looked for the companion of Polaris, but partly on 

 account of the nearly full moon, and partly from the thickness of 

 the diffraction-rings, I could not be sure of it. The moon was 

 perfectly steady ; with a power of sixty there was no trace of 

 twinkling at the terminator. I tried to see Titan, the largest 

 satellite of Saturn, but did not succeed. At the time it was not 

 certain whether this failure was due to the position of Titan with 

 relation to Saturn, or whether it arose from the blinding efful- 

 gence of the moon. Capella was perfectly steady, though there 

 was a slow change of colour from bluish to reddish, occupying 

 about a second. 



The succeeding night, at nine o'clock, though the sky was 

 mostly covered with cumulus clouds in motion southward, I 

 was astonished to find the terminator of the moon absolutely 

 free from twinkling and Arcturus down among the tops of the 

 dead aspen trees as steady as possible. The four diffraction rings 

 round the central disc were not perfectly circular, but that was the 

 fault of the lens. Every defect of centring or of surface and any 

 vein in the glass comes out even more clearly than in the work- 

 shop examinations, because, while the air is as steady, the light 

 is far more intense. 



I am certain, if a large telescope could be brought here and 

 maintained against the furious winds, great results might be 

 attained if there is much of this weather. But this particular 

 place is difficult of access, and possibly no better than other 

 situations on the line of the railroad. The sky is not as black 

 as I had expected ; it is rather of a light blue, though the full 

 moon makes much difference. 



On several other nights, in both lower and higher places, I 

 made observations, but never saw the combination of steadiness 

 and transparency again. On the plateaus at the foot of the 

 mountains and away from the groves of quaking aspen trees and 

 pines, the sun sends down scorching rays all day long on the 

 alkali plains, where only sage plants are sparsely scattered, and 

 even on horseback one can see the heated waves rising from the 

 ground. The air is far from being moist, for the lips are apt to 

 crack and bleed, and the mucous membrane of the nose is 

 parched. When the sun sets the ground rapidly radiates, and 

 we frequently had by morning one quarter of an inch of ice in 

 our vessels of water standing outside the tents. These plateaus 

 are on an average about 7,250 feet above the sea. The mere 

 fact of broken ground and wooded surroundings does not, how- 

 ever, suffice to produce, even at this season, a tranquil air ; for 

 when we rode over the Rocky Mountains, along the margin of 

 perpetual snow, to the head-waters of Snake River, and camped 

 at Trout Lake, nearly 10,000 feet high, though the air was ex- 

 ceedingly transparent, it was very unsteady. I rose at 4 a.m. 

 to see Venus, and her splendour was so great that it led to a 

 most delusive estimate of her apparent size. Occasionally, 

 during clear frosty weather in midwinter, a night of similar cha- 

 racteristics is seen at my observatory. On such an occasion I 

 obtaii ed, at the principal focus of the 15^-inch reflector, a 

 photograph of the moon near her third quarter in less than a 

 second. 



The officers of Fort Steele and the guides say it would be im- 

 possible to do any astronomical work in this region from the 

 middle of October till the middle of May, that is, for seven 

 months. The fierce winds, heavy falls of snow, and intense 

 cold would be unbearable. Even In the beginning of September 



