ch. n 



MICROSCOPE AND ACCESSORIES 



25 



Fig. 32. Projection Oculars with section re- 

 moved to show the construction. Below are 

 shown the upper ends with graduated circle to 

 indicate the amount of rotation found necessary 

 to focus the diaphragm on the screen. No. 2, 

 No. 4. The numbers indicate the amount the 

 ocular magnifies the image formed by the 

 objective as with the compensation oculars. 

 (Zeiss' Catalog.) 



'',. 41. Micrometer Ocular. — This is an 

 ocular connected with an ocular micrometer. 

 The micrometer may be removable, or it may 

 be permanently in connection with the ocular, 

 and arranged with a spring and screw, by which 

 it maj' be moved back and forth across the 

 field. (See Ch. IV.) 



Fig- 33 Fig. 34 



Figs. 33-34. Ocular Micrometer and movable scale. Fig. 33 is a side view of 

 the ocular while Fig . 34 gives a sectional end view, and shows the ocular micrometer 

 in position. In both the screw -which moves the micrometer is sho~wn at the left. 

 (From Bausch elf Lomb Opt. Co. ) 



i 42. Spectral or Spectroscopic Ocular. — (See Micro-Spectroscope, Ch. VI). 

 DESIGNATION OF OCULARS 



'/. 43. Equivalent Focus. — As with objectives, some opticians designate the 

 oculars by their equivalent focus ( j 15 ). With this method the power of the ocular, 

 as with objectives, varies inversely as the equivalent focal length, and therefore 

 the greater the equivalent focal length the less the magnification. This seems as 

 desirable a mode for oculars as for objectives and is coming more and more into 

 use by the most progressive opticians. It is the method of designation advo- 

 cated by Dr. R. H. Ward for many years, and was recommended by the committee 

 of the American Microscopical Society, (Proc. Amer. Micr. Soc, 18S3, p. 175, 1884, 

 p. 22S). 



