A THEORY OF THE DISPERSION OF LIGHT. 
21 
1 have stated some further particulars illustrative of the process. It is this method 
which I shall use in the present investigation, and therefore here merely quote the 
resulting formula from the last-mentioned paper. It is as follows ; 
— a t (^t< F [Jj b ) -J- b t 1 2 [/. i F -j- | M'b) • 
where the three indices of refraction are assumed from observation for the respec- 
tive rays B, F, and H, in the particular medium ; while p, is the index sought, any 
other of the four remaining of the seven standard rays, corresponding to which a t 
and b l are constants for the ray, independent of the particular medium, and which 
have been found from the values of \ in the paper last referred to, as follows : 
log a c = 1*95433 log b c = 2 7 65253 
log = 1*80441 log b D = 1*06281 
log a E = 1*49646 log b E = 1*03196 
log« Q = 1*74027* lo gb a = 1*62954*. 
The nature of the process of computation is obvious from an inspection of the for- 
mula ; and the data here stated will suffice for those who may wish to verify the cal- 
culations. I proceed to give the results in a tabular form, and then to offer such 
general conclusions as I think may be safely derived from them. 
Comparison of Refractive Indices from Cauchy’s Theory and from observation. 
1. Nitric Acid. 
3. Sulphuric Acid. 
Ray. 
Index 
observed. 
Index 
calculated. 
Difference. 
Ray. 
Index 
observed. 
Index 
calculated. 
Difference. 
B 
1-3988 
B 
1-4321 
C 
1*3998 
1-3998 
•0000 
C 
1-4329 
1-4329 
•0000 
D 
1-4026 
1-4024 
— -0002 
D 
1-4351 
1-4349 
— -0002 
E 
1-4062 
1-4058 
— -0004 
E 
1-4380 
1-4375 
- -0005 
F 
1-4092 
F 
1-4400 
G 
1-4155 
1-4156 
+ -0001 
G 
1-4440 
1-4448 
+ -0008 
H 
1-4211 
H 
1-4468 
2. Muriatic Acid. 
4. Oil Angelica. 
B 
1-4050 
B 
1-4836 
C 
1-4065 
1-4061 
- -0004 
C 
1-4863 
1-4849 
- -0014 
D 
1-4095 
1-4089 
- -0006 
D 
1-4887 
1-4882 
- -0005 
E 
1-4130 
1-4125 
- -0005 
E 
1-4932 
1-4924 
- -0008 
F 
1-4160 
F 
1-4963 
G 
1-4217 
1-4222 
+ -0005 
G 
1-5049 
1-5035 
— -0014 
H 
1-4265 
H 
1-5099 
* The two last numbers include the correction of an error which I detected in those given in the paper 
referred to. 
