26 



ELEMENTARY PHOTO-MICROGRAPHY. 



then be slid over every part of 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. 



The paraffin lamp and 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 condensing 

 lens are capable of being moved about together 

 without disturbing their relative position, one setting 

 is sufficient. Several good lamps on this system 

 can be bought, but an equally efficient arrangement 

 may be made, as shown in the sketch, fig. 10. 



in 



Fig. 10. 



Fig. 10 shows a simple wood frame (having a 

 circular hole for a paraffin lamp, and a slot in 



