146 



HELIOSTATS FOR THE MAGIC LANTERN [Ca. VI 



FIG. 77. ONE-MIRROR HELIOSTAT OF S'GRAVESANDE. 

 (From his: Elementa Mathematica Phy sices, Tomus II, Tabula LXXXIII). 



This picture is a facsimile except that the clock-shaft has been extended 

 above and below. 



B B Base of the mirror support with leveling screws. 



P Hollow cylinder in which the mirror support C can rotate. 



C The pillar with mirror fork at the upper end. 



5 Plane mirror. 



D K Shaft at right angles to the mirror and extending to the fork at the 

 end of the clock-hand (N 0). 



L L M Foot of the support for the clock-work. 



Ill The leveling screws of the support. 



