120 



THE USE OF THE MICROSCOPE 



lengths smaller than those by which they were called in 

 the catalogues, and which were marked on their mounts. 

 The optical tube length also, which influences the magnifi- 

 cation, is shorter with the low powers. Hence an objective 

 10 is one which produces an image 10 times the size of 

 the object, with the standard mechanical tube length. 

 Such an objective would have a focal length of about 16 

 millimeters. The new eyepiece magnification is equal 

 to the old multiplied by ^5-/^^ as the new magnifying 

 numbers of the apochromatic objectives are equal to the 

 old numbers multiplied by i^^5 (allowing for slight actual 

 changes in focus). 



Table of Calculated Limits of Reparation and Magnification 



Objective magnification 



Minimum 

 distance 



separable, 

 microns 



Maximum 



useful 

 magnifi- 

 cation 



Maximum 

 eyepiece 

 magnifi- 

 cation 



Aperture 



of 

 objective 



(W.I., water inmiersion; O.I., oil immersion; Mbn. I., monobromide of 

 napthaHn immension; FL, fluorite; c.c, correction collar.) 



