142 



HELIOSTATS FOR THE MAGIC LANTERN 



[CH. VI 



to turn the mirror around in a circle on its axis, and as a screw by 

 means of which it is raised or lowered on its hinges (fig. 75). 



235. Setting up the hand-regulated heliostat. The appara- 

 tus must be so placed that it receives the full sunshine on the 

 mirror. 



In the forenoon an eastern exposure can be used, and in the 

 afternoon a western one; or a southern one nearly all day. In 

 practice a person will naturally use the window best adapted to his 

 particular needs if he has a choice. 



SOLAR, PROJECTION MICROSCOPE OF ADAMS, WITH 

 PORTE-LUMIERE. 



(From Adams' Essays, 1771, PI. VI). 



Fig. 4 shows the movable mirror (K-L) placed outside the shutter in the sun, 

 0-P, screws in the square plate to fasten the instrument in the shutter; M-N; 

 thumb screws by which the mirror is turned to hold the sun's rays in the right 

 direction. The large tube, A-C-D, contains the condenser and receives the 

 shorter tube, fig. 5. Fig. 5 shows the tube into which the objectives are fixed. 

 If for large objects the lens (fig. 6) is screwed into the end, g, for smaller objects, 

 the objectives are arranged in a piece (fig. 8) sliding into the opening at q. 

 Notches along the objective slider indicate when the lens is centered. The 

 specimen to be examined is inserted at h. For high powers the substage con- 

 denser shown at fig. 7 is put in the tube between d-h. At b is a rack and pinion 

 for focusing the object. 



