262 
SECOND REPORT - 1832 . 
It may not be improper to observe, that if the above be a 
correct view of Prevost’s theory, it can hardly be conceived as 
otherwise than partially hypothetical. The idea, viz. that bodies 
even of a lower temperature than those about them actually 
give out a small degree of heat, is extremely difficult to con¬ 
ceive : and it does not appear absolutely essential to the ex¬ 
planation of the facts. 
Without reference to any theory, I venture to propose the 
following as the simple experimental law : 
All bodies of unequal temperature tend to become of equal 
temperature ; if in contact—by conduction; if at sensible di¬ 
stances—by radiation, of the excess of heat: and (in the latter 
case) whether the radiation reach the cooler body directly or 
by an intervening reflexion. 
This appears sufficient to include the facts of Pictet’s and 
Rumford’s experiments. 
7.) Alleged polarization of simple heat by reflexion. 
Mons. J. E.13erard(Memoire surles Proprietes des differentes 
Especes de Rayons qu’on pent separer au moyen du Prisme de 
la Lumiere solaire,” Mem. de la Societe d'Arcueil , Paris 1817, 
tome iii. See also Annals of Phil. O.S. ii. 164 ; Biot, Trade de 
Pliys. iv.) tried experiments for the polarization of heat. His 
apparatus was the same as Malus’s, having the axis of revolu¬ 
tion vertical; but no precautions of screening, &e. are men¬ 
tioned. He used an air thermometer containing a bubble 
of alcohol in the tube, in the focus of a reflector moving round 
along with the second glass: a ball of copper about two inches 
in diameter was in the focus of a reflector, placed in the posi¬ 
tion for polarization of light. (His experiments on heat with 
light will be referred to in another place.) He tried the effect 
with the metal heated below luminosity, and assured himself 
that there was a difference in the degree of heat reflected in the 
two rectangular azimuths of the second glass. 
I have attempted to repeat these experiments with the same 
kind of apparatus, carefully screened and arranged with the 
tube horizontal; but could produce no diminution in the proper 
position. ( Edinb . Journal of Science, N.S. vol. x. p. 207.) 
I also tried the experiment with a delicate mercurial thermo¬ 
meter, comparing this case with others (referred to in their 
proper place), in which light accompanied the heat; but in the 
former could detect no difference in a long series of repeti¬ 
tions. 
The total effect is in all cases extremely small, and the 
disturbing causes considerable, especially the heating of the 
