In the summer of 1872, Young spent several weeks at Sherman, Wyoming, at an elevation exceeding 8,300 feet. He carried with him the 9.4-inch telescope of Dartmouth College, where he was then professor, and this was the first expedition on which a large glass was used by a very skillful observer at great elevation. He found the number of good days and nights small, but the sky was exceedingly favorable when clear. Many 7th magnitude stars could be detected with the naked eye. Young's observations at Sherman were mainly spectroscopic, however, and they demonstrated the immense advantage of a high-level station, far above the dust and haze of the lower atmosphere. He pronounced the 9.4-inch glass at 8,000 feet the full equivalent of a 12-inch at sea level. Mont Blanc of 15,000 feet elevation was another summit where the veteran Janssen of Paris maintained a station for many years; but the continental conditions of atmospheric moisture and circulation were not favorable on the whole. Janssen was mainly interested in the sun, and the daylight seeing is rarely benefited, owing to the strong upward currents of warm air set in motion by the sun itself. Mountains in the beautiful climate of California were among the earliest investigated, and when in 1874 the trustees of Mr. James Lick's estate were charged with equipping an observatory with the most powerful telescope in existence, they wisely located on the summit of Mount Hamilton. It is 4,300 feet above sea level, and Burnham and other astronomers made critical tests of the steadiness of vision there by observing double stars, which afford perhaps the best means of comparing the optical quality of the atmosphere of one region with another. The writer was fortunate in having charge of the observations of the transit of Venus in 1882 on the mountain, when the Observatory was in process of construction, and the quality of the photographs obtained on that occasion demonstrated anew the excellence of the site. Particularly at night, for about nine months of the year, the seeing is exceptionally good, especially when fog banks rolling in from the Pacific, cover the valleys below like a blanket, preventing harmful radiation from the soil below.