102 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Sbr. 



The amplitude of the excursions of the images of the 

 Sun, Moon, and planets in a disturbed atmosphere is a vari- 

 able quantity that can not be determined but should be 

 avoided if practicable. To obtain the most trustworthy 

 results in reasonable time, we need the fixed observatories 

 located at points which conspire to give the best atmospheric 

 conditions determined upon after systematic and exhaustive 

 trial for special lines of research ; the highest class of instru- 

 mentation; observers with ideal eyes (of which unfortu- 

 nately there are very few) ; discrimination in the selection 

 of proper times of observation ; and a wise rejection of 

 observations made under abnormal conditions. 



Note. Since this paper was presented to the California Academy of 

 Sciences, Professor A. E. Douglass of the Lowell Observatory at Flagstaff, 

 Arizona, has published the second of his interesting papers upon "The 

 Atmosphere, Telescope and Observer," and "Scales of Seeing." Pop. 

 Astr. 1898. 



