THE MICROSCOPE, ETC. 



about to be described, and which we 



mend, fulfils all the requirements of the most expen"-"" 



sive sub -stage arrangements. 



Fig. 16 is a diagramatic representation of it in 

 section. 



In the rim R two screws are fitted, (only one is 

 represented in the figure for the sake of clearness) at 

 right angles to each other, opposite to them in the 

 interior of the tube a pretty strong spring S is 

 attached. 



By this means the ring A which fits on the pro- 

 jecting internal flanges of the rim R, can be moved 

 in any direction in the plane of the stage by the 

 screws, as the spring pressing against it on the 

 opposite side compels it to follow their motions. 



The diaphragm plate G is perforated with eight 

 holes varying from one half to one sixteenth of an 

 inch in diameter. In its centre is another aperture 

 quarter of an inch in diameter. Two thin plates half 

 an inch wide, through which the screw 7 fig. 16 

 passes, are placed above and below the diaphragm 

 before it is fastened in position, thus allowing it to be 

 displaced nearly quarter of an inch in its own plane, 

 and parallel to that of the stage, quite independently 

 of the remainder of the sub-stage apparatus. 



Any one possessed of ordinary skill and a few tools 

 for cutting sheet brass, will find little difficulty in ap- 

 plying this principle to existing instruments. 



From what has been previously mentioned with 

 regard to the resolution of certain structural pecu- 



