23 



tildes, gives the velocity of approach and recession 

 in kilometers per second. An investigation of this 

 kind threw much new light on the peculiar law of 

 the solar rotation, giving with high precision the 

 rotation period at different levels and the change 

 in its value from equator to pole. 



The Snow telescope thus proved its usefulness 

 for a wide variety of observations, most of which 

 we could not have made with moving telescopes 

 of the standard type. In addition to the work 

 already mentioned, the 1 8-foot spectrograph 



a 



i 



FIG. 16. Spectra of east (a) and west (6) edges of Sun, showing dis- 

 placement caused by solar rotation. 



yielded excellent photographs of spectra of various 

 parts of the solar disk, revealing numerous pecu- 

 liarities in the spectrum near the edge of the sun. 

 Although not designed for stellar work, the Snow 

 telescope also permitted photographs of the spec- 

 trum of Arcturus to be taken with a powerful 

 grating spectrograph. When compared with the 

 spectra of sun-spots, the relative intensities of the 

 lines were found to be similar, indicating that 

 Arcturus is cooler than the sun, a fact of impor- 

 tance in its bearing on the question of stellar 

 evolution. 



