79 
elevating post is 28 inches long, is of two-inch steel tubing, turned to fit 
the hole in the upright post. <A series of holes are drilled into the tubing 
to receive the sprocket wheel, which raises and lowers it. Upon top of the 
elevating post is a héad-post which receives the bed plate for carrying the 
camera and microscope. The head-post is turned to exactly fit the inside 
of the tube and permits the bed plate to be revolved on its horizontal axis. 
The bed plate is five feet long and five and one-half inches wide. It 
consists of a piece of three-sixteenths-inch rolled steel, to which is rivited 
’ 
two dressed half-inch steel tubes. These tubes are placed near each edge 
and give rigidity as well as serve for guides for the camera and micro- 
scope carriages. In the center of the bed plate is a rack for the adjust- 
ment of the camera and microscope. 
The attachment of the bed plate with the head post is by two dressed 
circular surfaces and a bolt. Upon the head post is mounted a screw 
which turns in threads cut upon the edge of the circular plate attached to 
the bed plate. By loosening the bolt and turning the crank upon the end 
of the screw the bed plate may be made to rotate upon its vertical axis. 
The carriages are twelve inches long, grooved to fit upon the steel 
