608 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the objective are divided by a doubly reflecting prism, known as the 

 ' Wenham prism,' so that one-half of the rays pass to an auxiliary eye- 

 piece mounted in a branch tube applied to the side of the main tube. 



In Microscopes of this class the prism has heretofore been mounted 

 in a box arranged to slide laterally in the lower part of the Microscope- 

 body, so that it could be moved into and out of its place by sliding 

 the box, and any imperfection in the bearings of the box, which are 

 necessarily narrow, allowed the box to move laterally, thereby impair- 

 ing the effectiveness of the instrument. Another serious objection 

 to the common method of mounting the prism is, that the size of tubes 

 in Microscopes being limited, and the box being contained entirely 

 in the tube or nose-piece, the movement of the box and size of the 

 prism are correspondingly limited. This being the case, a large 

 proportion of the rays which are transmitted by modern objectives 

 are prevented from passing to the eye-piece, so that it has frequently 

 been found necessary to remove the nose-piece containing the ordi- 

 nary prism-box and replace it by another nose-piece which had no 

 obstruction when the full effectiveness of the objective was desired. 



My invention is designed to obviate these difficulties by pro- 

 viding a prism-holder with a long cylindrical bearing, which is 

 readily made and practically indestructible by wear, and which admits 

 of either binocular or monocular arrangement of the Microscope 

 with the full effect of either method of vision. 



It consists of a prism-carrying arm fixed to the end of a spindle 

 extending through a sleeve passing through the side of the Microscope- 

 body, the spindle being provided with a milled head, by which it is 

 turned, and with a stop-pin, for limiting its motion. 



Fig. 90 is a vertical section on the line a; a; in fig. 91 of a portion 

 of a Microscope-body, showing my improvement applied. Fig. 91 is 

 a plan view, partly in section. 



The body of the Microscope is provided with a nose-piece A, 

 threaded in the usual way at its lower end to receive an objective, and 

 having sufficient depth to contain the prism-holder B. The prism- 

 holder B consists of a metallic plate a, bent twice at right angles, 

 and receiving between its parallel sides & c the prism C. The side c 

 of the holder B is prolonged, forming an arm c' which is secured in 

 any suitable manner to the end of a spindle D. In the present case 

 it is fitted to a shoulder on the spindle and fastened by means of a 

 small nut d fitted to the threaded end of the spindle. The spindle 

 D is fitted to a sleeve E, passing through the side of the nose-piece 

 A, so that it may turn therein without lateral or longitudinal motion. 

 To insure the perfect bearing of the spindle D in the sleeve E the 

 sleeve has a longitudinal slit e, which permits it to adapt itself to 

 the spindle by springing and to create the small amount of friction 

 necessary to retain the prism-holder in any position. The outer end 

 of the spindle D is provided with a nailled head F, by which tho 

 prism may be moved into or out of the field, and a pin /, projecting 

 from the spindle through a slot g in the sleeve E, limits the motion 

 of the prism-holder in either direction. The prism-holder B is 

 arranged relative to the main and auxiliary tubes of the Microscope 



