Remarks on the Formula for the Dispersion of Light. 117 



a and log. b for each ray, and the differences of the indices 

 of the assumed rays, which constitute the other Victors in the 

 equation (26.), [Loiul. Sf Edinb. Phil. Mag. for March 1836). 

 That equation in a general form for finding the index of any 

 ray ju., whose constants are a^ and b^ ; supposing the observed 

 indices for B F and H assumed, is as follows : 



The following values of log. a, and log. i, have been given 

 in the foregoing paper, 



log «p = T-80441 



log b^ = T-06281 



I have also received the following from the same source, 



log fl(j = l-'H3i5 

 logig = f-63384- 



It is easy to determine values of the same constants for the 

 other rays which remain to be found, viz. C and E. They 

 are deduced by the formulas (analogous to those in the former 

 paper, Eq. 15. 27. &c.), 



b, = — t,ll - 2^J. 



By substituting the values of t from I^'raunhofer's observa- 

 tions, we readily obtain, 



logfl!^, = 1-9.5433 



log b^ = 2-65253 



log Qj. = r-4964G 



logij; = r-03196 



With these logarithms, and those of the other factors in the 

 above equation for /x, which are derived from the three indices 

 f'B l*F i"'n assumed from observation for the particular me- 

 dium, we thus get immediately the values of /x^ for the other 

 rays resulting from the exact formula of theory. 



It would be easy to give examples of this method; but for 

 the present I shall confine myself to stating the results ob- 

 tained by it for the ray G in Fraunhofer's media ; compared, 



