THE RESOLVING POWER OF THE MICROSCOPE. 



25 



each of the humps and on corresponding portions of the same. 

 However, into this we need not enter here, the point principally 

 to be noted being that at least two of the light maxima must be 

 grasped by the objective, if the lines are to be seen separately. 



And now see how neatly this explains the newly observed fact. 

 Fig. 6 shows the intensity curve (a) when we have the light 

 passing through a number of lines, and (b) when we have it 

 passing through two lines only ; these curves are placed just 

 below one another in the diagram. The shaded part represents 

 the metal jaws above the objective, cutting down its N.A. 



You will observe that when the lateral humps of the curve are 

 quite cut off, there still remains a part of the lateral humps of 

 the curve b. This it is which suffices to account for the fact that 

 the two lines can still be seen resolved. If the reason is asked 

 why we could not see the parts of the lateral maxima when we 

 looked down the tube, it is simply because the light of the 

 dioptric beam or zero maximum was so intense that it drowned 

 the other. For we were looking at the zero maximum of twelve 

 lines, and at but a small part of the lateral maxima of two lines. 

 If precautions are taken so that the zero maximum observed 

 also proceeds from two lines only, the portions of the lateral 

 maxima can be readily seen. 



The above explanations and the figures refer to the case when 



