144 



REPORT — 1859. 



Assuming the space betweeu the eyes to be 2| inches, and the nearest 

 distance for distinct vision to be about 10 inches, we find 15° 48' as the 

 maximum stereoscopic angle. The possible shifting of the position of an 

 object on the lunar disc from east to west by libration in longitude may 

 amount to 15° 50', which is almost identical with the assumed maximum 

 stereoscopic angle, and the displacement from north to south, by libration in 

 latitude, never exceeds 13° 34', which falls within that angle. By the joint 



effect of a maximum libration in longitude and latitude, a point on the lunar 

 surface may, however, be shifted nearly 21°, which is greater than that under 

 which an object could be viewed by the eyes. 



* The centres of these diagrams should he 2f inches distant to give a stereoscopic picture. 



