46 ELEMENTARY PHOTO-MICROGRAPHY. 



the screen, after the projected image is thrown 

 upon it, to ascertain whether each part of the 

 object is equally in focus. 



When high powers of the microscope are em- 

 ployed, the rough side of the glass should have a 

 few places about the size of a shilling rubbed with 

 glycerine to render them transparent, whereby the 

 focussing of delicate fibres is found much more 

 certain. One should be put in each corner and 

 one in the centre. 



COMBINED LAMP AND BULL'S-EYE. 



The paraffin lamp and auxiliary condenser are 

 better mounted on one stand than when separate. 

 When used separately, the adjustments have to be 

 made every time, whereas when the lamp and con- 

 densing lens are capable of being moved about 

 together without disturbing their relative position, 

 one setting is sufficient. 



In photo-micrography success will not be ob- 

 tained without proper illumination, so that the im- 

 portance of first setting the bull's-eye in its right 

 place cannot be over-estimated. 



A lamp which sheds its light in every direction 

 would at best give only a feeble image in the 

 camera unless the scattered rays were collected and 

 directed by a lens towards the microscope. Now, 

 by using the bull's-eye, which is merely a plano- 

 convex lens, as a condenser, we may get the best 



