MOUNTAIN OBSERVATORIES IN AMERICA AND EUROPE. 5 



which I had occupied. In 1874 Mr. Lick proposed to found a moun- 

 tain observatory, and the first plans for the Lick Observatory were made. 

 An essential part of the programme was that the site should be selected 

 only after telescopic comparisons had been instituted between the 

 various stations proposed. Such an examination was actually made 

 by Professor Burnham in 1879, after the present site for the Lick 

 Observatory had been selected, but before any work had been done. 



The eclipse-expeditions of 1878 to the Eocky Mountain region, 

 familiarized many observers with the question ; and the expedition of 

 Dr. Langley to Mt. Whitney in 1881 exhibited the excellent con- 

 ditions to be obtained there. The first regular astronomical 

 observations were made at Mt. Hamilton (double stars ; the transit of 

 Mercury) in 1881, and the transit of Fe/iz^swas observed (photographed) 

 with excellent results in 1882. All these observations were published 

 and did their part in calling attention to the problem. The observatory 

 on Etna, built in 1881, but proposed by Professor Tacchini as early 

 as 1871, performed the same part in Europe. It may fairly be said 

 that the many mountain observatories now built, or building in all 

 parts of the globe owe much to the experience gained at the establish- 

 ments on Etna and at Mt. Hamilton, 



These establishments themselves are the legitimate outcome of the 

 proposal of Sir Isaac Newton in 1717, of the Malta expedition of 

 Lassell in 1852, and of the Teneriffe experiment of Piazzi-Smyth 

 in 1856. 



The inhabitants of the earth know the external universe directly, 

 only through the sense of sight; and our terrestrial views of the 

 planets and stars are much modified by the action of our own atmos- 

 phere upon the rays of their light which reach our eyes. We are, as it 

 were, immersed in an ocean of air, and one of the first j^roblems of 

 astronomical physics is to determine the effect of this overlying ocean 

 upon the light from external bodies which penetrates its depths. 

 Light moves in straight lines in empty space ; but light entering our 

 atmosphere is refracted from its course so that the ray which enters 

 our eye from a star no longer travels in its primitive direction. 



By the effect of refraction every star is seen not in its true place but 

 displaced. Moreover the atmosphere does not permit all the light of 

 the star to reach us. A certain quantity — percentage — is absorbed in 

 its passage through the atmospheric envelope, and the star appears 

 fainter to us in fact, than it would were the atmosphere removed. 

 It appears less bright near the horizon than near the zenith. Not 

 only is the quantity of incident light changed by the general absorp- 

 tion, but its quality is affected also by a selective absorption special to 

 our air. Bodies appear redder than they really are. The blue light 



