.-, 



6 THE MICROSCOPE. 



containing a pair of lenses, fitted within the body, 

 renders the compound microscope capable of an- 

 swering most of the purposes of a simple micro- 

 scope. 



Polariscope. An expensive but interesting and 

 useful addition to a microscope is a polarizing appa- 

 ratus, or polariscope. This consists of a Nicol's prism, 

 or a plate of tourmaline, placed beneath the stage, and 

 another in the body of the microscope or above the 

 eye-piece; both in brass fittings. The former is 

 called the polarizer, and the latter the analyzer. 



Rotating disk. Another most useful piece of ap- 

 paratus, for moving opake objects whilst under the 

 microscope, in all directions, is Smith and Beck's 

 " rotating disk." 



Slides. The slides upon which objects, especially 

 those to be viewed as transparent objects, are to be 

 placed, should be made of crown or plate glass. 

 They are usually 3 inches long, and 1 inch wide ; 

 but I prefer them 2J inches long, and 1 inch wide, 

 simply because they take up less room in a cabinet, 

 and because they do not project beyond the stage on 

 either side. They should not be more than ^th of 

 an inch thick, and as colourless and clear as possible. 

 The edges should be ground or filed, to prevent their 

 scratching the stage. 



Covers. The covers are square pieces of very thin 

 glass, less in breadth than the slides, so as not to 

 reach their margins ; and of various thicknesses, the 

 thicker and stronger being used to cover large ob- 

 jects for examination under the lower powers, and 

 the thinner serving to cover very delicate objects 

 requiring the higher powers. 



Side condenser. For illuminating opake objects, 

 a large plano-convex or doubly convex " bull's-eye " 

 lens, or side condenser, is used ; this is fixed to an 

 arm, which slides on a stand, so as to be capable of 

 being raised or lowered to a suitable height. This 



