104 ARRANGEMENT OP APPARATUS, ETC. 



the microscope is removed, and the camera arranged 

 vertically over the microscope, in the following man- 

 ner. 



The camera is fixed over the microscope by the 

 binding screw attached to the stand beneath it, the 

 conical bellows being removed from its front. The 

 round disc of light formed on the ground glass is 

 placed exactly central by means of the levelling 

 screws at each corner of the oblong board, to which 

 the camera is attached when this is accomplished, 

 the binding screw is tightened, and the conical bel- 

 lows slipped into its original position on the front, 

 of the camera. Great care is now required in at- 

 taching the end of the conical bellows to the short 

 tube of the microscope. It will be much more 

 easily done if the interior of the tube fixed to the 

 end of the conical bellows is covered with black 

 velvet, as well as its interior ; it will then slip 

 easily into that of the microscope, and the en- 

 trance of all light rays will be prevented. 



The image of the object is now roughly focussed on 

 the ground glass; the desired magnification obtained 

 by racking the ground glass backwards or forwards 

 to increase or diminish it, bearing in mind that the 

 actinic power of the light is said to decrease in pro- 

 portion to the square of the distance from its source. 



The part of the object we wish to focus should, 

 if possible, completely fill the plate ; this is some- 

 times impossible, as its thickness prevents the use of 

 lenses of sufficient power to magnify the lateral 

 dimensions, while their penetration defines those 

 parts lying on different planes. 



