328 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



the light source, and in its front wall aro two condensing lenses, which 

 render the issuing light rays parallel, or nearly so. The optical bench 

 takes the form of a pair of parallel wooden bars. For attaining the 

 different kinds of projection, two boxes equipped with lenses and mirrors 

 are provided— the vertical box and the episcopic box. These are used, 

 as required, singly or together in line, and are placed in front of the 

 issuing light beams. For direct projection there is also an objective 

 on a suitable carrier. 



Figs. 53 and 54 show how direct and vertical and microscopic pro- 

 jections are obtained. The " vertical box " is, in fig. 53, seen in situ, the 



Fig. 54. 



sloping mirror being arranged for throwing the light upwards through 

 a second condenser on to a different projection lens ; a sloping mirror 

 above this projects horizontally an image of any object placed in the 

 focus of the projection lens. When the mirror inside the vertical box 

 is clamped down, the whole of the upper part obviously passes out of 

 gear, the light passes out at the side of the box, and there is direct 

 projection. The change in position of the inside mirror is readily and 

 instantaneously effected. 



When used for microscopic projection, a lens is required for focussing 

 the light rays on to tho substago condenser, and the arrangement will 

 bo easily understood from fig. 54. The vertical projection apparatus 



