Objectives of the same power, but having different 

 angular apertures, will always have the same magni- 

 fying power and field. 



The fellowing table will probably be of assistance 

 to the beginner. After he has become better acquainted 

 with his instrument his judgment will dictate to him 

 what to do. 



A power of 25 diameters will show a surface of 

 about 1-5 inch diameter. 



A power of 50 diameters will show a surface of 

 about i-io inch diameter. 



A power of 100 diameters will show a surface of 

 about 1-20 inch diameter. 



A power of joo diameters will show a surface oj 

 about i-ioo inch diameter. 



A power of 1000 diameters will show a surface of 

 about i -200 inch diameter. 



This table is approximately correct with a Huy- 

 ghenian eyepiece. 



As has already been shown, magnifying power may 

 be obtained by using a higher power objective, or eye- 

 piece, or lengthening the tube, and it has also been 

 pointed out that the objective should be relied upon to 

 obtain this increase. 



Objectives with the same angular aperture, but of 

 different power, will have the same resolving power. 



