MICROSCOPIC OBJECTS. 183 



large condenser, which is attached to an arm that slides 

 up and down the rod which supports the candle-holder. 

 The figure A in the same engraving shows the manner 

 in which large shders are held upon the stage by means 

 of the forked finger- spring u u. 



The spring phial-holder p revolves within the tube 

 under the stage g, so as to give any inclination that may 

 be required. This phial-holder has a spring which forces 

 the glass vessel forward, and thus, while it possesses the 

 advantages of a safety slide-holder, enables us to use 

 vessels of any diameter less than that of the containing 

 tube. 



The polarizer fits into the socket or tube under the 

 stage g. This socket, which can be removed when not 

 in use, also serves to hold diaphragms, acliromatic and 

 other illuminators, &c. 



In employing a polarizing apparatus with this instru- 

 ment, the best construction for the analyser is the single- 

 image prism, which should be so mounted as to fit to the 

 body b close behind the object-glass d. By this arrange- 

 ment the field of view is always as large as the eye-piece 

 will admit. This is a very important improvement, made 

 by M. C. Chevalier upon Mr. Pritchard's original con- 

 struction. 



The traversing motions may be given. to an object in 

 this microscope either by the plan described in the * Mi- 

 croscopic Illustrations,' page 105, or that given in this 

 work, page 167. 



It is unnecessary here to describe the various kinds of 



