carer glass while dry, then separate slightly and, inclin- 

 ing the instrument, allow some of the oil to drop in the 

 space, then focus and read off. Divide the number of 

 graduations on the screw head by the pitch of the screw 

 and multiply by the number of divisio?is read off. 



Magnifying Power. This is a question of vital 

 importance in a microscope, not so much as a quality 

 in itself, as in connection with the resolving power. 

 The inquiry should not be simply, how many diameters 

 an instrument will magnify, but what the precision and 

 extent of its definition is under a certain magnifying 



2-3 inch Objective. 1-6 inch Objective. 1-12 inch Oil Immersion 



Objective. 



power. If a" high magnifying power is all that is 

 desired, this may be obtained to an almost unlimited 

 extent by means of simple lenses which may be pro- 



99 



