LIMITS OF OrXICAL CAPAClTiT OJF THE MICROSCOPE, 437 



straight lines; consequently, the diffraction effect of the light from 

 {a) at the point (i), apart from the factor A, which expresses its 

 total intensity, will be the same as that of the li-ht from a for the 

 point ,j. J3nt the latter can be calculated acccrding to the knowa 

 method valid for rectilinear rays. 



Pig. 2. 



B \ 



Let y y' be the relatively narrowest aperture, and (c) its middle 

 point, B the portion of the optical system immediately behind this 

 aperture, and let a be the image of the axis point a of the object; 

 further, let a /3 be its image lying in the medium y y' and / b 

 the image formed by B in the last medium. 



"When light proceeds from a, and is viewed through the aperture 

 y y whose radius is p, interference fringes will appear around a, 

 in which the distance S between each two neighbouring maxima, 

 (excepting the two first) will be according to known laws, if as- 

 before, a represents the divergence angle/? a y, which by assumption 

 is veiy small. 



2 p 



If JVbe the amplification of the image 5/ in comparison to a (d^ 

 the breadth of fringe d' of hf will be 



