52 ELEMENTARY PHOTO-MICROGRAPHY. 



the best effect will not be obtained. Moreover, 

 not only must the condenser be correctly centred, 

 but exactly focussed as well, otherwise the rays of 

 light which illuminate the object will not all 

 enter the microscope, but some will diverge in a 

 cone outside of it, and as it is only from the image 

 forming rays passing through the microscope that 

 a picture can be obtained, a considerable loss must 

 ensue with wrong adjustments. 



This will be made clear from diagrams (figs. 

 19 and 20). 



FIG. 19. FIG. 20. 



Objective and condenser correctly Condenser not focussed 

 focussed and centred. and not centred. 



O G, Objective. S, Slide. C, Condenser. 



When the condenser is stopped down by the iris 

 diaphragm, or otherwise made to correspond with 

 the aperture of objective used, and both condenser 

 and objective are focussed on the object itself, the 



