44 



PKACTICAL PHOTO-MICKOGKAPHY 



Mr. Gordon's method consists essentially of a ground-glass 

 screen, which is placed in the image plane and below the 

 eye-piece : the narrow beam of light is thereby dispersed in all 



directions, and is in fact 

 turned into a broad 

 bundle. It is due to 

 the rough surface of 

 the ground -glass that 

 the light is so dispersed, 

 and with a high-power 

 eye-piece this rough sur- 

 face is painfully evident 

 when observing the image 

 in fact, any fine detail 

 in the object is practically 

 obliterated. If, however, 

 this screen is given a 

 reciprocating motion, so 

 that the eye cannot appre- 

 ciate the rough details 

 of the ground -glass, the 

 image is then clearly seen, 

 and none of the disturbing 

 specks which otherwise 

 are evident can be 

 discerned. Mr. Gordon 

 has carried this method 

 to the extent of replacing 

 his eye-piece by another 

 microscope, so that his 

 eye-piece magnifies as 

 much as one hundred 



FIG. i2.-Projection Eye-pieces 2 and 4. diameters an amplifica- 

 ( full size.) tion of the image that is 



utterly impossible by any 



ordinary eye-piece method. It would appear that although 

 this arrangement has considerable experimental value, its 

 actual use in practice has yet to be determined. 



Fig. 12 shows the projection-oculars of Messrs. Zeiss, Nos. 2 

 and 4, in section. The lens A is the collective-lens, and when the 



