ARRANGEMENT OF APPARATUS, ETC. 105 



The most satisfactory magnification being ob- 

 tained, we pass the silk cord round a bevelled ring 

 attached to the fine adjustment of the microscope, 

 and the wheel on the rod. passing under the camera 

 stand. The focussing glass previously adjusted, is 

 applied to that part of the image on the ground 

 glass, requiring the most accurate definition. The 

 best focus is obtained by observing the appearance 

 of the structure through the focussing glass during 

 the revolution of the milled head attached to the 

 rod connected with the fine adjustment. 



The chemical focus is found when the object 

 appears clearly defined, although its markings are 

 surrounded by a red areola, (see previous pages). A 

 black cloth is now hung over camera and stand, but 

 not reaching lower than the stage of the microscope; 

 the blue glass or sulphate of copper cell placed be- 

 tween the bull's eye condenser and the mirror ; and 

 an opaque card between the two latter, to enable the 

 exposure to be given at the proper time. 



We now proceed to the dark room, and having lit 

 the lamp, observe the condition of the trays and 

 measures, their position, and that of the various 

 bottles containiug solutions. 



The barrel should contain a good supply of fresh 

 and pure water; the tin box containing the dry 

 plates is placed on the floor or a shelf, on the oppo- 

 site side of the dark room, to that occupied by the 

 washing trough and lamp. 



We recommend the use of dry plates twice as 

 fast as ordinary collodion in this case, as the in- 



