1853.] OF THE ROYAL INSTITUTION. 259 
was cast so liberally upon the waters. I rejoice, Ladies and Gentle- 
men, in the opportunity here afforded me of offering my tribute to 
the greatest worker of the age, and of laying some of the blossoms 
of that prolific tree which he planted, at the feet of the great dis- 
coverer of diamagnetism.” 
Dy 
WEEKLY EVENING MEETING, 
Friday, February 18. 
Tar Duxe or NortHuMBERLAND, K.G., F.R.S., President, 
in the Chair. 
G. G. Sroxzs, M.A., F.R.S., Lucasian Professor, Cambridge. 
On the Change of Refrangibility of Light, and the exhibition thereby 
of the Chemical Rays. 
Berrore’ proceeding to the more immediate subject of the Lecture, 
it was necessary to refer to certain discoveries of Sir John Herschel 
and Sir David Brewster, more especially as it was the discovery by 
the former of these philosophers of the epipolic dispersion of light, 
and of the peculiar analysis of light which accompanies the pheno- 
menon, that led to the researches respecting the change of re- 
frangibility. 
When a weak acid solution of quinine is prepared, by dissolving, 
suppose, one part of the commercial disulphate in 200 parts of water 
acidulated with sulphuric acid, a fluid is obtained which appears 
colourless and transparent when viewed by transmitted light, but 
which exhibits nevertheless in certain aspects a peculiar sky-blue 
colour. This colour of course had frequently been noticed; but it 
is to Sir John Herschel that we owe the first analysis of the pheno- 
menon.* He found that the blue light emanates in all directions 
from a very thin stratum of fluid adjacent to the surface, (whether it 
be the free surface or the surface of contact of the fluid with the con- 
taining glass vessel,) by which the incident rays enter the fluid. 
His experiments clearly shew that what here takes place is not a 
mere subdivision of light into a portion which is dispersed and a 
portion which passes on, but an actual analysis. For after the rays 
have once passed through the stratum from which the blue dis- 
persed light comes, they are deprived of the power of producing the 
* Philosophical Transactions for 1845, p. 143. 
