706 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



about it the rope running to the counterpoise makes one turn ; the re- 

 mainder of the rod is octagonal ; by turning the rod with the hand the 

 camera may be moved up or down with great delicacy, while the rod 

 offers no hindrance to the direct and more rapid movement of the 

 camera by hand. 





ImN 



Fig 135. 



Fig. 136. 



Fig. 137 shows the apparatus fitted to the Microscope, the illumina- 

 tion being provided in this case by a Thomson 90° arc lamp, lantern- 

 condenser, and alum-cell. The Microscope must be attached to a 

 levelling plate which is a cast-iron slab 17 by 25 mm. and 6 mm. thick, 



