558 SUMMARY OF CURRENT RESEARCHES RELATING TO 



solid table and the camera firmly secured to the platform, as shown in 

 the illustration. The Microscope (from which the eye-piece has been 

 removed, and the tube, lined with a roll of dead black paper) is to be 

 inclined to a horizontal position and firmly secured to the board by 

 turn-buttons, with the end of the body inserted in the cone front of 

 the camera, about the joining of which a piece of black cloth or velvet 

 is to be wrapped to exclude all extraneous light. The lamp is now to 

 be lighted and raised to such a height as will bring the flame exactly 

 even with the centre of the stage, the direct light being used without 

 the mirror, which must be removed. It is presumed that the proper 

 object-glass has already been attached to the microscope-body, and 

 that an achromatic condenser has likewise been inserted in the sub- 

 stage. A Kellner eye-piece answers admirably for this purpose. A 

 secondary condenser is sometimes necessary between the lamp and 

 stage, as shown in the woodcut, to secure a bright and even illumi- 

 nation all over the focussing screen. This accomplished, the object 

 to be photographed is placed upon the stage, secured in position by 

 the clips or slides, and focussed, which is readily done with the coarse 

 adjustment, for the bellows of the camera being still closed, one can 

 observe the image on the screen and manipulate the milled head of the 

 adjustment at the same time. 



The image having been accurately centered on the screen, the 

 bellows is to be extended until the desired magnification is reached, 

 when it will be found that its sharpness is considerably reduced, 

 whilst the screen has been removed so far from the object that it is 

 impossible to readjust the focus and observe the image at the same 

 time without some special appliance, controllable from the screen end 

 of the camera. A very simple contrivance has been adopted in this 

 case, which works with the utmost smoothness and delicacy. A 

 groove is turned in the periphery of the fine adjustment screw, around 

 which a small cord is passed, and carried through a succession of 

 screw-eyes on either side of the base-board to the rear, where a couple 

 of small leaden weights are attached to its ends, thus keeping the cord 

 taut. A very slight pull on either side, whilst the eye is fixed upon 

 the image on the screen, suffices to adjust the focus with the utmost 

 exactness. A glance at the illustration will show the arrangement of 

 this focussing cord, which is applicable alike to stands having the fine 

 adjustment screw on the nose-piece or at the rear of the compound body. 



Since no ground-glass has a sufficiently fine surface to admit of 

 really sharp focussing of the image, with even moderately high 

 powers, the final adjustment is made as follows : — The front and back 

 of the plate-holder having been removed, a sheet of plate glass the 

 size of the gelatine plate to be used is inserted, and the holder 

 adjusted to the camera, when, by means of a focussing glass placed 

 against the outer surface of the plate, a sharp and accurate adjustment 

 can be made in a moment, after which nothing remains to be done 

 toward securing the negative but to substitute (in the dark room) a 

 sensitive plate for the plain glass, attach the holder to the camera, 

 p,nd make the exposure. 



