MOUNTAIN OBSERYATOEIES IN AMERICA AND EUROPE. 

 By Edward S. Holden. 



INTRODUCTION. 



The main object of tlie present paper is to study the conditions 

 suitable for astronomical work at high levels. It has been necessary to- 

 examine the records of meteorological mountain-stations to obtain 

 some of the required data ; and the physiological questions involved 

 could not be passed over, since, after all, the observer must be at the 

 full height of his powers if he is to advance Science. But meteoro- 

 logical and physiological questions are here quite subordinate to the 

 main purpose of the paper, which relates chiefly to purely astronomical 

 matters. 



It is interesting to note the expansion of the ideas connected with 

 telescopic obsei'vation. Galileo and Kepler, (1609), considered the 

 telescope alone. It was an optical instrument. "When it wa>3 perfect, 

 nothing more needed consideration. Newton (1717), whom nothing 

 escaped, saw that vision might be better in the pure air of high 

 mountains. 



If the theory of making telescopes could at length be fully brought into pra c- 

 tice, yet there would be certain bounds beyond which telescopes could not perform. 

 For the air through which we look upon the stars is in a perpetual tremor, as 

 may be seen by the tremulous motion of shadows cast from high towers, and by 

 the twinkling of the fixed stars. The only remedy is a most serene and quiet air, 

 such as may perhaps be found on the tops of the highest mountains above the 

 grosser clouds. * 



Sir William Herschel was the first to consider the observer as a 

 part of the apparatus. In 1782 he points out that to obtain the best 

 results the observer, the air, and the instrument must be of one temper- 

 ature. In 1794 he says, while re-observing the belts on Saturn and 

 i noting changes that had occurred : "I took care to bend my head so 

 as to receive the picture of the belts in the same direction as [formerly] 

 — as there was a possibility that the vertical diameter of the retina 

 [might be more or less sensitive than the horizontal one." 

 *Optics, second edition, 1719, p. 107. 



