254 
LIGHT AND RADIANT HEAT. 
Roth pencils 
issuing from 
Iceland crys- 
tal, had like 
properties. 
lie found it the maximum of heat, the elevation of temperature above that 
Bemr^rs abso- the surrounding air, was only one-fifth of what it was in the 
lute heat was ex treme red rays. The absolute intensity of heat produced 
lower. 
was also less in the experiments of Berard, than those of Hers- 
chel. Do these differences depend on the material of the 
prisms and diversity of the apparatuses, or on some other phy- 
sical circumstance, inherent in the phenomenon itself ? On 
this we cannot decide. 
M. Berard was desirous of knowing whether these properties, 
obtained separately in each of the pencils into which a ray of 
light is divided when it traverses a rhomboid of Iceland crystal. 
He passed a beam of solar light through a prism formed of a 
piece of the same kind of crystal. Each of these two spec*’ 
trums presented the same properties. In both of them the 
calorific property was gradually less from the violet to the red, 
and it still subsisted beyond the limits of the visible rays. 
Consequently, whether this faculty be inherent in the luminous 
rays themselves, or be foreign to them, it is divided along with 
them when they are separated by the crystal. 
But in these operations, the luminous rays are polarized by 
the crystal. Do the obscure calorific rays undergo a similar 
In order to determine this, M. Berard received the solar 
ray on a polished and transparent glass, which polarized part of 
them by reflection. This reflected ray was afterwards received 
on a second glass, fixed on an apparatus which allowed it to be 
turned round the ray with a constant incidence, and lastly, this 
incidence was itself so determined, that in a certain position of 
the glass, the reflection ceased to take place. We know, from 
the experiments -of Malus, that a glass can always be So dis- 
posed as to answer this condition. This being effected, M, 
Berard received the calorific and luminous rays after the reflec- 
tion from a second glass upon a (concave) mirror, and by di- 
recting them upon a thermometer, he found that when the 
When the light luminous reflection took place, the thermometer rose, and con- 
was wholly sequent ly the heat was reflected also : but in the case where, 
transmitted, * J * 
the heat was so in consequence of the position of the second glass, the light 
The radiant 
caloric is re- 
flected along 
with the light, effect ? 
and polarized 
like it. 
likewise. 
passed through without reflection, the heat was 
transmitted at 
the 
