168 Mr KELLAND, ON THE DISPERSION OF LIGHT, 



Now the refractive index m varies inversely as the velocity ; hence we 



may put -^ under the form 



1 100,000.0 1,000,000./ , 



-.-P ^ -^ y:^ nearly, 



where p = A^ {<p{r) + ^^ Sx'} Sp\ 



(100,000)^ q = ^ A-E {<p{r) + ^^ Safl Sp\ 



(100,000)^/ = %A-2 {0(r) + ^ Saf\ Sp\ 

 A being some constant factor. 



I have extracted from the article on Light in the Encyclopedia 

 Metropolitana the values of X for the seven fixed lines, as determined 

 by M. Fraunhofer, and have also taken the values of m given by the 

 same author for seven kinds of glass and three fluids, water, solution 

 of potash, and spirit of turpentine. 



For each of these substances we shall have seven equations between 

 2), q and I, with the known values of m and X. I have always de- 

 termined 2h q, I from the equations given by the lines (B), (E) and 

 (H"), and by substituting the values of the last two quantities, q and 

 / in the other equations, have determined from them values of j). 



The verification of our formula consists in the near coincidence of 

 the values of p with each other. The rest will be easily understood 

 from the following tables. 



100,000 J 1,000,000 „ ^, 

 Table I. contains the values of X, — —„ — and for the 



X' A 



different fixed lines expressed in parts of a Paris inch : they are 

 multiplied by some power of 10 merely to avoid decimals. 



