MAGNIFYING POWER OF A MICROSCOPE. 



243 



Tests with Powell & Lealand's Low-angled ^in. Objective. 



Other Tests with ^-in. Objective. 



Notice how nearly alike the eyepiece constant is for each pair 

 of tests when different tube lengths are used, but the same eye- 

 piece and objective. The last pair are practically the same, 

 although the tube lengths vary to an extraordinary extent. 

 Mr. Nelson says that "they are all done with extreme accuracy 

 by projection. In every case the Ramsden's disc was found and 

 the screen placed ten inches from it." The magnifications were 

 250 and 94 diameters. 



There is another easy way in which the information given by 

 the " eyepiece constant " may be used for determining the total 

 magnification for any tube length. Suppose, for example, the 

 eyepiece constant has been obtained with a given objective, eye- 

 piece, and tube length, a record being made ; then it is only 

 necessary to work a very simple proportion sum to determine at 

 any time the total approximate magnification with any tube 



