3 02 



DIFFRACTED LIGHT IN MICROSCOPY 



[CH. IX 



FIG. 178-179. DIFFRACTED LIGHT IN MICROSCOPY. 

 (From Wright's Principles). 



Fig. 178. Object (grating) lighted with a narrow beam (/) from the condenser 

 and giving off diffracted rays which are brought to a focus with the dioptric beam 

 (I) above the objective in part (full lines); and in part forming diffracted beams on 

 each side above the objective (broken lines). These diffracted beams not brought 

 to the same focus as the dioptric beam cause imperfections or confusion in the 

 image. 



Fig. 179. Small diaphragm (C D) below the condenser focused on the grating, 

 A B, and from this point the diptric beam (solid white) and diffracted light (broken 

 lines) extend through the objective and finally focus at B' A'. By looking at the 

 eye-point with a magnifier the image of the back lens shows not only the diaphragm 

 image (D f C'), but secondary images of the same (D' C' and D" C"). See small 

 figure in the middle also. 



