HELIOSTATS FOR THE MAGIC LANTERN [Cn. VI 



FIG. 79. UNIVERSAL, ONE-MIRROR HELIOSTAT. 

 (From the Catalogue of R. Fuess). 



Modified by extending the clock-shaft above and below and by adding the 

 abbreviations in and rf for the incident and reflected ray on the mirror (M). 



This heliostat is called universal for it is adjustable so that it can be used in 

 any latitude and at any season of the year. See fig. 80 and 241 for further 

 explanation. 



The dials showing the time and declination may be used for 

 setting the heliostat, but one can get the apparatus set accurately 

 by trial as just described. If the time and declination scales are 

 to be used one must consult a nautical almanac for the sun's 

 declination for the given date, and an accurate clock for the time 

 of day. 



242. For centering the magic lantern when a heliostat is used 

 the same general principles must be followed as with the arc light 

 magic lantern (Ch. I, 51-57, fig. i, 74). 



To center the light one must be able to adjust the mirror by hand 

 after it has been set to follow the sun. This is provided for in all 



