MOUNTAIN OBSERVATORIES. 395 



it might be said, into a science apart. Its pursuit is, at any rate, far 

 too arduous to be conducted with less than a man's whole energies : 

 while the questions which it has addressed itself to answer are the 

 fundamental problems of the new physical astronomy. There is, how- 

 ever, but one opinion as to the expediency of carrying on solar inves- 

 tigations at greater altitudes than have hitherto been more than tempo- 

 rarily available. 



The spectroscope and the camera are now the chief engines of solar 

 research. Mere telescopic observation, though always an indispensa- 

 ble adjunct, may be considered to have sunk into a secondary position. 

 But the spectroscope and the camera, still more than the telescope, lie 

 at the mercy of atmospheric vapors and undulations. The late Profess- 

 or Henry Draper, of New York, an adept in the art of celestial pho- 

 tography, stated in 1877 that two years, during which he had photo- 

 graphed the moon at his observatory on the Hudson on every moonlit 

 night, yielded only three when the air was still enough to give good 

 results, nor even then without some unsteadiness ; and Bond, of Cam- 

 bridge (U. S.), informed him that he had watched in vain, through no 

 less than seventeen years, for a faultless condition of our troublesome 

 environing medium.* Tranquillity is the first requisite for a successful 

 astronomical photograph. The hour generally chosen for employing 

 the sun as his own limner is, for this reason, in the early morning, be- 

 fore the newly emerged beams have had time to set the air in commo- 

 tion, and so blur the marvelous details of his surface-structure. By 

 this means a better definition is secured, but at the expense of trans- 

 parency. Both are, at the sea-level, hardly ever combined. A certain 

 amount of haziness is the price usually paid for exceptional stillness, 

 so that it not unfrequently happens that astronomers see best in a fog, 

 as on the night of November 15, 1850, when the elder Bond dis- 

 covered the " dusky ring " of Saturn, although at the time no star 

 below the fourth magnitude could be made out with the naked eye. 

 Now, on well-chosen mountain-stations, a union of these unhappily 

 divorced conditions is at certain times to be met with, opportunities 

 being thus afforded with tolerable certainty and no great rarity, which 

 an astronomer on the plains might think himself fortunate in securing 

 once or twice in a lifetime. 



For spectroscopic observations at the edge of the sun, on the 

 contrary, the sine qua non is translucency. During the great "In- 

 dian eclipse" of August 18, 1868, the variously-colored lines were, 

 by the aid of prismatic analysis, first descried, which reveal the 

 chemical constitution of the flame-like "prominences," forming an 

 ever-varying, but rarely absent, feature of the solar surroundings. 

 Immediately afterward, M. Janssen, at Guntoor, and Mr. Norman 

 Lockyer, in England, independently realized a method of bringing 

 them into view without the co-operation of the eclipsing moon. 



* " American Journal of Science," vol. xiii, p. 89. 



