CH. IV] 



MAGNIFICATION AND MICROMETRY 



Demonstrate the difference in magnification due to the distance at 

 which the image is projected, by raising the microscope so that the 

 distance will be 350 millimeters, then lowering to 150 millimeters. 



In preparing drawings it is often of great convenience to make 

 them at a distance somewhat less or somewhat greater than the stand- 

 ard. In such a case the magnification must be determined for the 

 special distance. (See the next chapter, § 181.) 



For discussion of the magnification of the microscope, see : Beale, 

 pp. 41, 355 ; Carpenter-Dallinger, p. 288 ; Nageli and Schwendener, 

 p. 176 ; Ranvier, p. 29; Robin, p. 126 ; Amer. Soc. Micrs., 1884, p. 

 183 ; 1889, p. 22 ; Amer. Jour. Arts and Sciences, 1890, p. 50 ; Jour. 

 Roy. Micr. Soc, 1888, 1889. 



■ 



OCULAR 



37 or 5° mm - 



OCULAR 



25 mm. 









Objective. 



TUBE 

 IN 



Tube 1 '»•„„„ 



MM. 1 



Tube 

 out 



MM. 



Ocular Micrometer 



Valuation, 

 tube in. out mm. 





X 



X 



X 



X 









X 



— 



X 



X 



x 









X 



X 



X 



X 









X 



X 



— 



X 



X 









X 



x 



x 



X 









X 



X 



X 



X 







Simple Microscope. 



X 





16- 



FiG. 102. 

 Table of Magnifications and of the Valuations of the 



Ocular Micrometer. — The above table should be filled out by each 

 student. In using- it for Micrometry and Drawing it is necessary to keep 

 clearly in mind the exact conditions under which the determinations were 



