194 SCIOPT1CON MANUAL. 



It consists of an ordinary microscopic glass slip, of greater 

 thickness and size than usual, with a spherical cavity about 

 three quarters of an inch across, and one-sixteenth of an 

 inch deep, ground and polished in the middle of one face. 

 This, when in use, is closed by a thin glass cover, which is 

 kept in place by adhesion and atmospheric pressure, the 

 cavity beneath it being filled with water containing the insect 

 or other object. 



If it is desired to use high powers, we must be contented 

 with a limited selection of objects, choosing such as are 

 strongly defined and well colored. Diatoms, blood-disks, 

 or other objects which are delicately tinted or colorless are 

 quite unfit for such use. A strongly colored eye of a fly, 

 sting of a wasp, or other part of an insect, such as a claw 

 of a spider, answer well. 



In this case I have obtained the best results with Zent- 

 mayer's T% objective, using an extra condenser, consisting 

 of a plano-convex lens of about three inches focus, and an 

 inch and a half in diameter, placed about an inch back of 

 the object. 



This greatly increases the illumination of the field. 

 In using the gas microscope, much depends upon the 

 efficiency and convenience of the support for lenses and the 

 stage, or what is known commonly as the " gas microscope 

 attachment." 



The microscope attachment for the Sciopticon is repre- 

 sented by the following wood cut. 



The microscope body, to which the 

 objective is attached by a sliding tube, 

 is fitted to the grooved arm, and moved 

 by rack and pinion for accurate focus- 

 ing, similar to our best table micros- 

 copes. This curved arm is fastened to 

 the stage plate, which is attached to 



