CH. VI] 



HELIOSTATS FOR THE MAGIC LANTERN 



153 



FIG. 81. TWO-MIRROR HELIOSTAT WITH THE MOVABLE MIRROR AT THE 



END OF THE CLOCK-SHAFT. 

 (From the Catalogue of Max Kohl). 



The figure has been modified by extending the clock-shaft and by adding the 

 second mirror and the light rays. This heliostat is usually fixed for a given 

 latitude, hence in ordering one, the latitude of the place should be given. It 

 could be made adjustable for latitude, but that would naturally increase the 

 cost. 



N-P, L The clock-shaft pointing to the celestial north pole above, and 

 indicating the angle corresponding with the latitude below. 



c Clamp to hold the mirror (M) to the revolving clock-shaft. 



M Movable mirror. It is adjusted in the fork and on the clock-shaft until 

 the reflected rays proceed parallel with the earth's axis, hence also parallel with 

 the clock-shaft. 



M 2 The fixed mirror to be set by hand in the beginning. 



S and the Arrows. The sun's rays. 



