Ill 



A power of 100 diameters will show a surface of 

 about -g*Q inch diameter. 



A power of 500 diameters will show a surface of 

 about yJo- inch diameter. 



A power of 1000 diameters will show a surface 

 of about ^i-Q- inch diameter. 



This table is approximately correct with a 

 Huyghenian eyepiece. 



As we have already shown, magnifying power 

 may be obtained by increase of power in objective,, 

 eyepiece, or increase of tube length and have also 

 pointed out that the objective should be relied upon 

 to obtain this increase. 



Objectives of the same angular aperture, but of 

 different povvers, will give identical results by bring- 

 ing them up to the same magnifying power, unless 

 the difference is considerable. In both objectives 

 and eyepieces the lenses decrease in size with the 

 increase in power and consequently give less light 

 and while this one objection exists in the objective, 

 an additional one occurs in the eyepiece, in that 

 the eye must be brought closer to the eye-lens and 

 must be kept more strictly in the optical axis r 

 which at a long sitting, becomes fatiguing. 



Choice of eyepiece should be determined by 

 requirements and individual preference. All re- 

 sponsible manufacturers and dealers make up such 

 outfits of stands, objectives and eyepieces, as ex- 



