DESCRIPTION OF THE ACHROMATIC MICROSCOPE. 95 



Table of Magnifying Powers. 



_, , T Magnifying powers, estimated by a 



Focal Leng.hs. 



standarf of sight. 



Inches and Parts. Diameters. Surface. 



1 ...... , ....... 10 .......... 100 



3-4ths .......... 15 .......... 225 



*- l-2nd .......... 20 .......... 400 



l-3rd .......... 30 .......... 900 



l-4th .......... 40 .......... 1,600 



l-6th .......... 60 ......... 3,600 



MOth .......... 100 .......... 10,000 



l_15th .......... 150 .......... 22,500 



l-20th .......... 200 .......... 40,000 



l-30th .......... 300 .......... 90,000 



l-40th .......... 400 .......... 160,000 



l-50th .......... 500 .......... 250,000 



l-60th ., ........ 600 .......... 360,000 



l-80th ......... 800 .......... 640,000 



1-lOOth .......... 1,000 .......... 1,000,000 



Previous to placing the magnifier into the arm just 

 mentioned, the triangular bar should be raised, the 

 object put upon the stage, and the light reflected from 

 the mirror made to pass through it. All this is more 

 readily effected before the lens is fixed in its position. 



Some persons prefer having stops or diaphragms under 

 the stage, when making observations with single lenses. 

 In this case, the aperture of the magnifier maybe greatly 

 increased ; for the stops, so situated, will have the same 

 effect of reducing the diameter of the emergent pencil of 

 light as a restricted aperture in the mounting of the lens 

 would do, whilst the vision for deep powers is rendered 

 by it more agreeable. 



