Mounting Media of High Befr activity. By H. G. Madan. 281 
better. The most hopeful direction in which to look is towards 
compounds containing either or both of the radicles naphthyl and 
phenyl, in which, as Dr. Gladstone’s researches have shown, the 
carbon-atoms are so situated in the molecule as to cause exceptionally 
high refractivity in the resulting compound. 
Table of Optical Constants of some Highly Refractive 
Organic Substances. 
Name of Substance. 
* 
u 
H a 
% 
% 
y 
Temp. 
Cent. J 
Coefficient of 
Dispersion 
Meta-cinnamene (or Metastyrol) 
1-592 
1-597 
1-612 | 
1-624 
■ ° 
15 
0*032 
Quinidine 
1-596 
1-602 
1*621 
1*639 
15 
0-043 
Phenyl thiocarbimide 
1-646 
1*654 
1-681 
1-706 
10 
0-060 
o-Monobromonaphthalene f 
1-649 
1-658 
1-682 
1*704 
20 
0-051 
Naphthyl-phenyl-ketone.. 
1-659 
1-669 
1-697 
■ t 
15 
.. 
Piperine 
1*665 
1-681 
1-734 
1*806 
18 
0-141 
Methylene di-iodide 
1-732 
1-743 
1*767 
1*794 
; 15 ! 
0-062 
Solution of sulphur in methy-l 
lene di-iodide . . . . . . . . / 
•• 
1-778 
•• 
16 
•• 
Solution of phosphorus in me-1 
thylene di-iodide (equal l 
weights of each) ) 
: 1-929 
1*944 
1-984 
j 2-021 
18 
0-092 
* The observations of the hydrogen liues were made with an “ end-on * ’ vacuum 
tube, a form which was first proposed by Prof. Piazzi Smyth, and which gives a 
remarkably brilliant hydrogen light. 
f B. Walter, Ann. Phys. und Cliem. [N.F.], 1891, p. 511. 
X It was found impossible to observe H y , owing to the strong absorptive power 
of the substance for the more refrangible part of the spectrum. 
