THE RAINBOW DVK R) A CIRC[jr,AR SOURCE OF LIGHT. 23 



TABLE III. {Continued). 



In tlie case of slit and cylinder, the method of mechanical 

 quadrature is simpler ; the mean value of /" in the interval 

 y.d — y'h and y.d + /A> representing the vahie of Fi at xf^. Pernter's 

 method of calculation which we have described in § 1 is appli- 

 cable in this case only. He calculated the case where ?' =0.025 

 cm., and corapared^'^ with our result, shows that there was no 

 great difference in both results. This fact shows that there is 

 no great difference in the two cases, of slit-cylinder and of 

 circle-sphere. Thus, fortunately, Pernter's method of calculation 

 applies as a rough approximation for the case of circle-sphere, 

 though his reasoning was not exact. It seems rather curious 

 that in his calculation for ?'=0.05 cm., we can not find the 

 general nature in § 7 ; when the interval of consecutive maxima 

 or minima of F is less than ^"l", the maxima and minima 

 interchange. 



(Ij Wien Sitz. Ber. CXIV. 2a, p. 13 (1905). 



