THE BOOK OF THE LANTERN. 219 



crowned with a grooved wheel, which is geared by a piece 

 of cord to another similar wheel at the end of a focussing- 

 rod, which is brought within easy reach of the plate- 

 carrier outside the box. 



These various arrangements will be rendered clearer by 

 reference to the diagram, where O is the objective, S the 

 stage, F the focussing-rod, L the lamp, C the condenser, 

 and A the frame holding the gelatine plate, or the 

 focussing -glass, as the case may be, for one takes the 

 place of the other. And let me say, in passing, that this 

 method of withdrawing one glass so that the other can 

 take its exact place, is the best that could be adopted, for 

 the merest fraction of difference in register would be 

 perceptible in photo-micrographic work, while it might 

 remain undiscovered in negative taking of the ordinary 

 kind. 



Mr. White's apparatus was, at the time I saw it, fitted 

 with a 1-inch objective; but he told me that he had 

 used higher powers with it. It certainly is capable of 

 very fine work, as was proved by an album full of speci- 

 mens which he exhibited. His focussing-screen was a 

 plain glass, ruled with -lines by a diamond, and he 

 employed a focussing eye-piece. But it is evident that, 

 with this method of working, the operator could employ 

 an opaque screen, such as a piece of opal glass, for the 

 room in which the work is carried on takes the place of 

 the camera, and he is practically within it, and can 

 look upon the side of the screen which is next the 

 light. By means of a scale upon the sliding-board which 

 carries the gelatine plate, it is easy to note, without actual 



