176 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 



Galilean Telescope. (Figs. 679 and 680.) This consists of 

 a single convex glass, whose focal length is from four to eight 

 inches for an object glass, and a double eoncave lens from 

 a half to two inches focus for the eye-glass. The distance 



Figs. 679 and 680. 



between the two glasses is equal to the difference of their 

 focal lengths, and their power is in the ratio of their foci. 

 They are usually mounted in brass cases, japanned on the 

 outside, having one, two, or three draws on slides, which are 



