10 DR. GLADSTONE ON THE EEFE ACTION -EQUIVALENTS OF THE ELEMENTS. 
period seems now to have come at which it is wise to put on permanent record the 
results at which I have hitherto arrived. I shall give therefore first the data, and then 
the deductions in reference to each element examined. 
The Data. 
These consist of the observations of Dulong* on the refraction of gases, of Malus, 
Brewster, and othersf on solids, and of DelffsJ, Jamin, Sauber§, Landolt ||, Haagen% 
and Ivetteler** on liquids, in addition to such determinations as I have myself made, 
whether previously published ff or not. 
Most of my fresh experiments have been made with a new instrument constructed by 
Mr. Browning, with a horizontal instead of a vertical circle, and several other improve- 
ments. 
I have continued to measure the solar lines A, D, and H, whilst Landolt has pre- 
ferred the three bright lines of the hydrogen spectrum. I have calculated the refrac- 
tion for the line A, as being the most free from whatever influence there may be con- 
nected with dispersion, and the German professor has reckoned for hydrogen a, which 
is identical with the solar C. These rays are so near together that the difference can 
scarcely affect the first place of decimals in a refraction-equivalent. When the deter- 
minations are made with greater precision, it will be for physicists to decide which shall 
be finally adopted. 
In the subjoined Tables the actual refractive indices are given, and the refraction- 
equivalents as calculated from them. For the complete data, I must refer to the papers 
of the several observers, and to Appendices I., II., and III., where my own new expe- 
riments are tabulated. 
Table I. — Simple Elements. 
Elementary substance. 
Condition. 
Part of spectrum. 
Refractive index. 
Authority for index. 
Refraction-equivalent. 
Carbon 
Diamond 
Bright 
2-470 
Brewster, &c. 
5-18 
Solid 
Red 
2-4603 
Schrauf. 
4-85 
Sulphur 
Bright 
203 
Various. 
160 

Liquid 
A 
1-9024 
Gladstone and Dale. 
15-98 
Solid 
D 
1 -9295 
16-47 
Phosphorus 
D 
2-1168 
18-98 
„ 
Liquid 
A 
2-0389 
,, 
18-27 
,, 
D 
20746 
18-89 
Bromine 
Gaseous 
A 
1-6260 
Gladstone. 
16-23 
Chlorine 
Bright 
1-000779 
Dulong. 
8-87 
Hydrogen 
,, 
„ 
1-000138 
,, 
1-53 
Oxygen 
„ 
„ 
1-000272 
301 
Nitrogen 
” 
” 
1-000300 
” 
3-30 
* Annales de Chimie, xxxi. p. 154. f Ency. Brit., Article “ Optics.” 
X Pogg. Annalen, lxxxi. p. 470. § Ibid, cxvii. 577. 
I! Ibid, cxvii. 353, cxxii. 545, cxxiii. 595. Ibid, cxxiii. 125. 
** Ibid, cxxiv. 390. 
ft The papers of Mr. Dale and myself in tbe Philosophical Transactions, 1858, p. 887, and 1863, p. 317 ; 
Phil. Mag. July 1859 ; also Brit. Assoc. Report, 1863, Trans. Sec. p. 12 ; my paper in Journal Chem. Soc. 1865, 
p. 108 . 
