262 PROCEEDINGS OP THE AMERICAN ACADEMY 



from a drawing made by a camera obscura or camera lucida, or from 

 a photograj^h ; and has the advantage that it begins to be accurate for 

 depressions greater than 2^ or 3° just where they pass out of the 

 ranore of the micrometer-level as described above. 



Valuable observations on the changes in the dip and in the refrac- 

 tion might be made with a large telescope of this form. It is much to 

 be desired that such observations might be conducted for a period of 

 years from two such stations as Mount Washington and Portland. 

 As the pressure, temperature, and moisture of these points is already 

 determined by the Signal-Sei'vice Department, a small additional 

 expense would furnish a valuable addition to our knowledge of the 

 atmospheric refraction. 



