THE WOODWARD ILLUMINATOR. 171 



*' make-shift " arrangement. With the prism thus 

 mounted any movement of the object-slide will of course 

 cause a corresponding movement and decentering of 

 the prism; furthermore, such object-slides can only be 

 well examined when posed in nearly the horizontal 

 position on the stage; it often, too, occurs that the 

 intermediate drop looses its hold, suffering the prism to 

 slide or even to loose its attachment entirely; and then,, 

 again, I have frequently got the very best work when 

 the facet of the prism was slightly depressed from the 

 under surface of the slide. 



It is far better, then, and for the reasons given, to 

 have the prism mounted, and to those who propose to 

 adopt my method of illumination, I will say that much 

 depends on the proper mounting, and that any piece of 

 sub-stage apparatus which shall impede the passage of 

 rays from the lamp to the mirror, or from the mirror 

 to the prism, will defeat the maximum working of the 

 latter. Hence, as a rule, it cannot be well mounted in 

 the usual sub-stage, the latter obstructing too much 

 light. 



After much experiment, and with the hearty co-opera- 

 tion of Mr. Sidle, I am now in possession of the Wood- 

 ward prism, suitably mounted and adapted to the " his- 

 tological" of Mr. Zentmayer, as will be seen from 

 inspection of the cut on the following page. 



This accessory, as above delineated in plan and sec- 

 tion, is easily placed in position on any of the histolo- 

 gical stands. Provision is also made for centering in a 

 lateral direction. The prism can also be revolved so as 



