ELEMENTARY PHOTO-MICROGRAPHY. 57 



light used for high powers, we take parallel rays 

 from the bull's-eye after the paraffin lamp has been 

 set according to the instructions previously given. 

 The eyepiece is next taken out and a piece of white 

 cardboard placed about I2in. away from the end of 

 the body tube to act as the screen, and receive a 

 projected image from the microscope. The disc of 

 light will possibly be found brighter in one part 

 than another. The lamp is moved sideways until 

 the whole disc is equally illuminated, with the 

 object well denned in the centre. The focussing 

 may be altered for this purpose. The eyepiece is 

 replaced to see if the field be still uniformly lighted, 

 a slight adjustment of focus again being necessary. 

 If the lamp be in the right position, the disc of 

 light will be sharp and uniform right up to the edge 

 of the circle with or without an eyepiece. The card- 

 board is taken away, and the camera brought up 

 to the microscope, with the velvet connecting tube 

 over the eyepiece. 



This tube may be made of cardboard lined 

 with black velvet. It should slip over the eye- 

 piece, and project about an inch. A short tube, 

 say fin. long, should also be placed in the brass 

 mount of camera that usually carries the lens, 

 and its diameter must be a Jin. less than inside 

 of the eyepiece tube, so that when the camera 

 is slid up to the microscope, a light-tight 



