comes to the center and will be in focus, if not exactly, 

 at any rate very closely. This statement should per- 

 haps be modified in so far that as the nose-piece is 

 rotated each objective should be approximately in focus 

 when in position, since objectives and nose-pieces are 

 still supplied by makers with which this is not the case. 

 Of all the convenient accessories these are the most 

 useful and in most common use, the writer knowing 

 from experience that nearly all of the instruments sold 

 for personal use are supplied with the double nose- 

 piece when two objectives are used, and the triple 

 when three are taken. 



Bodies or Tubes. These are of two kinds: 

 monocular, having one body which may contain one 

 or two draw-tubes, observations being made with one 

 eye, and binocular for observation with both eyes, the 

 two tubes being fixed together at the nose-piece and 

 gradually separating until they reach the pupillary 

 distance. The first is a monocular microscope, the 

 second a binocular microscope. 



While the methods for transmitting the rays from 

 the objective to the binocular tubes vary, the construc- 

 tion in most common use is that introduced by 

 Mr. Wenham. 



By reference to Fig. 30 it will be seen that the rays 

 from one-half the objective are transmitted uninter- 

 ruptedly to the vertical tube, while the prism intercepts 



44 



