DESCRIPTION OF THK ACHROMATIC MICROSCOPE. 95 



Table of Magnifying Powers. 



, , Magnifying powers, estimated by a 



Focal Lengths. * lo'.inch standard 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 



l-10th 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 



l-100th 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. 



