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228 General Notes. [ February, 
the exact topographical relations of a complicated object withlow | 
magnifying powers that the microscope affords with higher pow- — 
urther, only a single plano-convex lens 2.5°™ in diameter, 
is required for an enlargement varying at pleasure from five to 
fifty diameters. Professor His employs as an objective a stereo- | 
scope-head (of Dallmeyer), or a small Steinheil aplanat (No, 1), 
The instrument consists of a heavy circular iron base, from 
the center of which rises a brass rod, marked to centimeters, half 
centimeters, and millimeters. On this rod are seen the mirror 
M), the object-table (7), the objective (O), and the camera | 
lucida (), all supported by horizontal bars that move on sliding 
ferrules, The mirror is placed as near the base as conveniente | 
will allow, and its supporting bar is 7.5°™ long. The bars bearing | 
the other pieces are all of corresponding length, and the sliding — 
ferrules can be fixed at any point by the aid of set-screws. The 
ferrules of the mirror and the object-table are made of such 
length that when in contact with each other and resting on the 
highest part of the base, they are in the position required for the 
lowest magnifying power. In this position the object-table has- 
an elevation of 11™, the objective 18.5, and the camera 2 
above the lower face of the base, or what may be called” 
drawing plane. +e 
Thus placed the focal distance is 7.5°™, and the camera 15! 
the normal position of the drawing plane, and endeavors: 
made to provide the instrument with such a lens. 
The magnifying power may be increased in several 
-cm 
p] . 
Wig form has been found more convenient than the rectangu!ar form g 
