426 Royal Society of Edinburgh :—Prof. Forbes’s Experiments 
by some authors, were afterwards fully confirmed, and some ano- 
malies which they presented, explained, by Robison, Englefield, 
Berard, Seebeck*, and Melloni. 
Heat, then, even unaccompanied by light, appears to be capable 
both of reflection and refraction. But new modifications of light, 
discovered of late years, require us to investigate how far the ana- 
logy may be pursued. In 1802, Dr. Young announced his remark- 
able discovery of the interference of the rays of light, or the power 
of two luminous rays, properly disposed, to produce darkness by their 
union, About the year 1808, Malus, a most eminent French phi- 
losopher and mathematician, discovered the remarkable modification 
which light undergoes by reflection from certain substances at cer- 
tain angles. This modification may be easiest conceived by stating 
the fact, that light so reflected becomes incapable of undergoing a 
second reflection in certain positions of the reflecting surface, when 
common light would be reflected. 
The corresponding experiment in the case of heat was tried by 
Berard, along with Malus, about the year 1811, and an account of 
them was published in 1817, in the Mémozres d’ Arcueil. They found, 
that when the solar beam was twice reflected in the manner just 
stated, the heat and light refused simultaneously to be reflected in 
certain positions of the second reflector. The same experiment was 
repeated with incandescent bodies, with the same result ; and even, 
as stated by Berard, with bodies having temperatures beneath that 
of visible incandescence. These experiments were probably discon- 
tinued in consequence of the death of Malus, and the details were 
never published, if, indeed, they were ever carried to any great ex- 
tent. The result has been, that Berard’s conclusion seems not to 
have been generally adopted by the scientific world. The po- 
larization of heat has remained amongst the doubtful facts in sci- 
ence. It has been adopted in scarcely any systematic works, 
whether British or foreign: and, of late years, direct evidence 
seemed to be entirely against it. Professor Powell of Oxford, re- 
peatedly and fruitlessly, attempted to obtain Berard’s result. No- 
bili of Florence (whose recent loss science has to deplore) attempted 
it likewise with the aid of his thermo-multiplier, an instrument ad- 
mirably adapted for the measurement of small quantities of heat ; 
and Melloni having failed to polarize even luminous heat by tourma- 
lines, concurs in the conclusions of Powell and Nobili. The Vice- 
President then observed, that it was under these circumstances that 
the subject was undertaken by Professor Forbes, who, by means of 
arrangements differing from any that had before been used, has suc- 
ceeded in completely establishing the polarization of heat under all 
the circumstances in which light is polarized, namely, by Reflection, 
Transmission, and Double Refraction, and that it is for the esta- 
blishment of these facts that the Keith Prize has been awarded by 
the Council}. 
* Seebeck’s memoir on this subject will be found in Phil. Mag., First Se- 
ries, vol. lxvi. p. 330. e¢ seg.—Enrr. 
+ Prof. Forbes’s paper establishing these facts will be found at large in Lond. 
and Edinb. Phil. Mag., vol. vi. p. 134, e¢ seg. See also vol. vii. p. 349.—Enir. 
