on the Refraction and Polarization of Heat. AQT 
Dr. Hope then stated that, in the ordinary case of the publication 
of papers, the Society holds itself in no degree responsible for the 
truth of the facts stated therein; but, in the adjudication of prizes, 
the case is different; and that, with regard to them, the Council 
are bound to be satisfied of the truth of the statements for which 
they award their prize. Several memhers of the Council had seen 
and satisfied themselves of the accuracy of Mr. Forbes’s leading ex- 
periments before the Keith Prize was awarded ; and, some days ago, 
he deemed it right to request Mr. Forbes to show him the more im- 
portant of these experimental demonstrations. ‘This he succeeded 
in doing in a way which left upon his mind not the slightest doubt 
as to the truth of his results ; the variations of temperature being so 
obviously displayed, as to prevent the slightest ambiguity as to the 
true source from which they are derived. The instrument employed 
in the research is the thermo-multiplier, of which the invention is 
due to Nobili, though it has been greatly improved for experimental 
purposes by Melloni. Professor Forbes has likewise increased greatly 
its power of indicating the more delicate effects by employing a te- 
lescopic apparatus, which enables him to measure a quantity of heat, 
perhaps not exceeding one fifteen hundredth part of a degree of 
Fahrenheit. 
That the Society may fully understand the nature of the proofs 
afforded by Mr. Forbes’s experiments, reference must be made to 
the correlative facts observed in the case of light. 
When light undergoes reflection from glass at an angle of 56°, its 
physical character is found to be thus far altered, that it refuses to 
bea second time reflected by another plate of glass placed to receive 
the ray at the same angle of 56°, if the plane of incidence on the 
second glass be perpendicular to the plane of incidence on the first. 
The light is then wholly transmitted by the second plate. If the 
plane of incidence be the same for the two plates, complete reflec- 
tion takes place at the second plate. This illustrates polarization by 
reflection. 
If a number of glass plates be used, and light transmitted obliquely 
through such a bundle of plates, it is in like manner found, that the 
emergent light is wholly transmitted by a second similar bundle 
placed parallel to the first, but is almost wholly reflected, and therefore 
not transmitted, when the second bundle is placed so that whilst the 
ray falls upon it at the same angle as upon the first, the plane of in- 
cidence on the second bundle is perpendicular to the plane of inci- 
dence upon the first bundle. This is polarization by transmission or 
refraction. 
Lastly, It was observed before the close of the 17th century by 
Huyghens, that certain bodies, as Iceland spar, endowed with the 
property of double refraction, alter at the same time the character 
of the light in thetwo refractedrays. So that,if two sections similarly 
cut from a crystal of Iceland spar be placed upon one another in 
conformable positions, or the respective positions which they occu- 
pied on the crystal, the two rays will proceed through the second 
slice as they did through the first, and be refracted according to the 
