THE WOODWARD ILLUMINATOR. 173 



in a moment's time. All the necessary motions are pro- 

 vided for, and it may be depended on for first-class 

 performance. 



From what has already been stated, it is almost need- 

 less to repeat that when either of the mountings de- 

 scribed are to be used on the histological or acme stands 

 the sub-stage must be removed. It is quite possible that 

 the mountings presented may, with slight modifications, 

 be fitted to other microscope stands. 



The form of prism (angles 98, 41 and 41), as sug- 

 gested by Col. Woodward, will be found to do very 

 acceptable work. It occurred to me, after having had 

 considerable experience with this accessory, that there 

 was nothing gained by having the acute angles equal, 

 but on the other hand advantages would be insured by 

 an inequality of these angles, either of which might be 

 used as occasion required. I therefore begged Mr. Sidle 

 to make me a prism with an obtuse angle of 93, one of 

 the acute angles to be 47, the other to be 40, and this 

 is the form I have adopted, believing it .to be the most 

 seviceable .arrangement yet proposed, and especially 

 adapted to the general run of modern wide-apertured 

 objectives. To provide one's self with two or more 

 forms of prisms will not involve serious expense. Either 

 of the mountings 1 have described can be modified so 

 that the prism can be removed and others substituted 

 in its place. 



To use the Woodward prism we will suppose on the 

 acme stand first, screw the accessory into the well- 

 *hole of the stage securely ; next, place the slide to be 



