TJie Relation of Aperture and Power. By Prof. Abbe. 473 



(2.) So far as the medium powers are in question, which are 

 below the limits of useful powers for the maximum apertures, but 

 still above those amounts which could be obtained by very 

 moderate apertures, a somewhat strict economy of aperture is 

 indicated by important considerations in regard to the general 

 demands of scientific work (penetration, working distance, &c), 

 because the disadvantage of superabundant aperture will be always 

 greater than the possible benefit. For the medium powers in 

 use, the figures of Table I. will therefore give the approximate 

 limits of latitude which may be deemed reconcilable with a 

 rational construction of the Microscope for scientific work. 



(3.) Concerning the lower and lowest powers, a gradually in- 

 creasing latitude is left for the application of wider apertures than 

 would be theoretically necessary in regard to the delineating 

 capacity required for these powers. A surplus of aperture in- 

 creasing up to about 100 per cent, for the lowest amplifications, 

 will be in favour of the illuminating power of the Microscope ; a 

 considerably greater excess will at all events be mere waste.* 



* The concluding part of the paper — ii. Division of the Entire Power of the 

 Microscope between Objective and Ocular — will be printed in the next number of the 

 Journal. 



