COLLINS'S UNIVERSAL CONDENSER. 



183 



a shutter diaphragm. This addition to the microscope 

 can be used with any instrument and without a sub- 

 stage, and is on this account easily adapted to the 



FIG. 115. Collinses Webster's Universal 

 Condenser. 



Shutter Diaphragm seen separately. 



cheaper forms of microscopes. Its advantages are, 

 that it is moderately cheap, is at once an achromatic 

 condenser, parabolic illuminator, and graduating dia- 

 phragm and polariser. By means of a lever, the 

 central aperture can be gradually closed, and, pro- 

 vided the object-glass has sufficient "resolving power," 

 it facilitates the resolution of the 

 more difficult test-objects. With a 

 " spot-lens stop" the object is illu- 

 minated on a dark ground, and 

 when high powers are used in con- 

 nection with the polariscope, the 

 advantage derived by such an ad- 

 dition to the ordinary mode of 

 illumination is considerable. 



Mr. Hyde's " Condenser " is con- 

 structed for use with immersion 

 objectives, having apertures greater 

 than correspond to 180 in air. The 

 lens is a right-angled prism, having 

 a plano-convex lens fitted in an up- 

 right, and mounted in brass to slip into the sub- stage 

 (fig. 116), will condense parallel rays to a focus on a 

 balsam-mounted object, through a slide of average 



FIG. 116. Hyde's Illu- 

 minator. 



