CH. VI] 



HELIOSTATS FOR THE MAGIC LANTERN 



159 



FIG. 84. LENS AND PRISM HELIOSTAT OF ALFRED M. MAYER. 

 (From the Catalogue of Optical Instruments by R. Fuess), 



The figure has been modified by extending the clock-shaft above and below. 

 As here shown the instrument is suitable for any latitude. It uses a mirror 

 instead of a second prism as in the original of Mayer (fig. 83). 



U Clock-work. 



N P, L The clock-shaft extended to indicate the direction of the celestial 

 north pole above, and below the angle of elevation corresponding to the lati- 

 tude of the place where the instrument is used. 



P D Z Three divided scales; P for the latitude, D for the Sun's declination, 

 Z for the time of day. 



S, k and Pr. The convex and the concave lens, and the prism as shown in 

 fig- 83. 



Sp Mirror to take the place of the prism (L) in fig. 83. 



