CH. VI] HELIOSTATS FOR THE MAGIC LANTERN 



157 



FIG. 83. LENS AND PRISM HELIOSTAT OF ALFRED M. MAYER. 

 (From the American Journal of Science, Vol. 154, iSg 1 ^). 



This heliostat is in principle like the two-mirror heliostat with the movable 

 mirror attached to the end of the clock-shaft (fig. 81). 



J Biconvex lens about 10 cm. (4 in.) in diameter to receive the sun's rays 

 and render them convergent. 



K Concave lens to render the converging beam parallel. 



g Rack and pinion movement to change the position of the concave lens 

 and thus increase or diminish the size of the beam. 



/ Right-angled prism receiving the parallel bundle from K and reflecting it 

 to a fixed prism (L) or to a mirror, by which it is reflected in any desired 

 direction. 



The two lenses J K and the prism /, are all on one common axis and are 

 rotated by the clock-shaft G, and thus made to follow the sun like the mirror 

 on the end of the clock-shaft in figure 81. The clock-shaft G must be at an 

 elevation corresponding to the latitude of the place (see also fig. 84). 



