ARRANGEMENT OP APPARATUS. 133 



ter on account of not evaporating, allows of a greater 

 length of time for arrangement of apparatus, and a 

 more protracted exposure. An equal mixture of 

 both will be found most suitable. 



The proper focus and correction for cover glass 

 obtained, the eye-piece tube is removed, and the 

 sleeve securely fastened round the short tube, by a 

 strong elastic band in addition to that already in- 

 serted in its orifice. 



Before proceeding with this description, it should 

 be mentioned, that the most favourable position for 

 the condenser is about one and half to twice its focal 

 length from the object, and the sliding diaphragm is 

 undoubtedly the best to use with this and all higher 

 powers. The best sized hole is that which, when 

 brought into focus, is slightly smaller than the field. 



The fine adjustment wheel is screwed off, and the 

 screw passed through a small hole in the sleeves. A 

 light rod attached to a cork,* as before described, is 

 fitted to the wheel; this is now returned to its 

 original position on the microscope. 



The camera, from which the oblong board and 

 conical bellows front have been removed, is attached 

 to an ordinary camera stand, and placed so that an 

 image of the object may be properly received on the 

 focussing screen. 



The distance of the screen, owing to its not being 

 continuous with the microscope, is only limited by 

 the length of the dark room. Practically it will be 

 found that perfect results are not obtained when it 



* See Appendix. 



