26 PRACTICAL MICROSCOPY. 



For oblique illumination a very thin stage has been 

 devised by Mr. Wenham ; it has only one top-plate, with 

 rectangular and concentric rotary movements worked by 

 two milled heads upon the same axis. This stage has two 

 set-screws by means of which it can be easily and effec- 

 tually centered. It is bevelled on the edge and graduated 

 to serve as a goniometer. By releasing a strong clamp-nut 

 this stage can be at once removed and any other sub- 

 stituted. 



The swinging substage attached to the " International " 

 microscope stand of Messrs. R. and J. Beck may be seen 

 in Fig. 7. It is mounted perfectly true with the body, and 

 is moved up and down in its fitting by means of milled 

 heads. In this fitting all the varied appliances for modi- 

 fying the character and direction of the light are fitted. 

 The bar into which the substage fits is itself attached to an 

 arc working in a circular fitting, and is capable of rotation 

 by means of a milled head, so that it may be carried round 

 and above the stage if necessary. The amount of angular 

 movement may be recorded from the graduated circle. 

 The lower triangular bar carries the mirror when the illumi- 

 nation is required to be concentric with the optical axis of 

 the instrument ; when desired it can be made to slide on 

 the substage bar, and then can be moved above or below 

 the stage in the same manner as the substage, Messrs. 

 Swift and Son have produced what they term a " Radial 

 Traversing Substage Condenser," in order to produce the 

 same results in illumination as can be obtained with swing- 

 ing substages. Mention only is made here, as its construc- 

 tion and use will be fully explained when treating of 

 accessories. 



Messrs. Watson and Sons, of Holborn, have recently 

 patented the arrangement, an illustration of which is shown 

 in Fig. 1 6. In this the mirror is accurately centered, while 



