330 Prof. F. L. 0. Wadsworth on the Resolving Power of 



will be given by an expression similar to (9), but containing 

 a term /(<£) which represents the distribution of intensity in 

 the source of radiation. 



The law of distribution (in a normal source) is not yet 

 definitely known. The one ordinarily assumed is that which 

 follows from Maxwell's kinetic theory, which is * 



M =e-** 2 (17) 



where k is a constant whose value varies with the substance 

 emitting radiation, and with the temperature and pressure in 

 the source. A law of distribution more recently proposed by 

 Michelson is f 



M)=e^.. ..... (18) 



If the first law is assumed, we have for the intensity in the 

 diffraction-pattern 



/vfoo 



'■J ' 



sin' 



77 



(7-*) 



,-*£2. 



{I*-*} 



^d(j> = ylr l {fc,y, a ,); . (19) 



and if the second, 



I 



7T 



sin 2 rcf) sin 2 - (y — <j>) 



Fig. 4. 



-<ty = *,(r,7,«,)- • (20) 



I have not succeeded in integrating either of these integrals 



* See Rayleigh, Phil. Mag. April, 1889, p. 298 ; also Michelson, Phil. 

 Mag. September 1892. 



f i Astrophysical Journal,' Nov. 1895, p. 251. 



