TEE AH EQUIP A STATION. 



519 



fails to record stars wliich will appear when an exposure of five or six 

 hours is used. For the comparatively bright stars, the number in- 

 creases approximately by the ratio three for each magnitude. For 

 example, there are about three times as many stars of the second 

 magnitude ag of the first, and three times as many of the third magni- 

 tude as of the second. There are indications, however, that this ratio 

 is not kept up for the fainter stars, that is, there are not three times 

 as many stars of the sixteenth as of the fifteenth magnitude. No limit 

 to the universe has yet been reached, however. With the Bruce tele- 

 scope stars can ho ]iliotographed too faint for vision in the greatest 



-*- ^ 



m 



The Meteorological Station on El Misti. 19,000 ft. 



telescopes of our day; but increase in exposure always brings out new 

 and fainter stars, until the practical limit of the exposure is reached 

 in the fogging of the plate by the diffused light of the sky. The 

 longest exposure yet made in this observatory was with the Cooke lens, 

 an exposure of twenty-four hours, on four different nights. Such 

 an exposure in such an instrument brings out with great perfection 

 the wonderful beauty of the cloud-forms of the Milky Way. 



Since the establishment of the Peruvian station, meteorology has 

 formed an important, though subordinate, part of the work. For 

 about ten years a line of auxiliary stations was maintained, reaching 

 from the Pacific across the Andes to the low country on the upper 

 waters of the Amazon. The culmination of this series was the station 



