346 



H. NAGA0KA; DIFFRACTION PHENOMENA 



dark space ; we shall by the above described process be able to obtain 

 a series of lines of equal intensity due to these sources. In the 

 diagrams (Figs. 8 and 9 PI. XVII) I give a portion of these lines in 

 the immediate neighbourhood of the rim of the luminous source 

 (a= oo) when there is a dark circular space (a=40); the lines are drawn 

 for the same difference 0.1 of the intensity. Fig. 8 represents the 

 lines when the dark disc touches the rim, and Fig. 9 when the nearest 

 distance d between the rim is 1. In both figures, the boundaries of 

 the luminous source are shown by dotted lines. 



The inspection of these figures shows that when the dark space 

 is in geometrical contact with the rim of the luminous source, it 

 appears only as a dark protuberance from the surrounding dark space 

 into the luminous source ; with the receding of the dark space towards 

 the interior of the luminous source, the connecting ligament ' becomes 

 thinner and finally falls away. The inner dark space is a little elongat- 

 ed and assumes a pear-shaped appearance, while the external dark 

 space bulges out towards the luminous source. The change is 

 however transient ; with further ingress, the dark disc becomes cir- 

 cular and the swelling of the external dark space vanishes away. It 

 must not be forgotten that the image of the dark disc is generally less, 

 than actually would be the case, and the edge of the luminous source 

 will extend a little into the dark space. To show the successive stages 

 of these protruding dark discs, I give the following diagrams (Fig. 4) y . 



Fig. 4. 



■ 40 = 



5 = 0.2 



5 = 0.5 



