144 Professor Fores on the Refraction 
24. The following are the general results of my experiments 
on Tourmaline. 
Source of Heat. No. of Comparisons. Proportions of Heat polarized by 
A and B E and F Tourmalines A and B Eand F* 
Argand lamp, - 3 16 per cent. 
Oil lamp, . - 7 3 14 percent. 11 ... ... 
Incandescent platinum, 4 3 Dip cts oss eae ce 
Brass at 700°, - 7 (1 negative) Dee ins. 
I cannot, therefore, entertain any doubt on the polarization of 
heat by tourmaline, notwithstanding the opposite result which 
M. Metviont (and I also at first) obtained. 
25. Some very curious considerations arise from the study of 
these facts. Since 84 per cent. of the heating rays of an Argand 
lamp pass through the second tourmaline in the case where the 
light is entirely stopped, we must adopt one of two conclusions : 
either that the heat which necessarily accompanies light is exces- 
sively small, or else that radiant light during its instantaneous 
passage through a medium, is capable of being converted into ra- 
diant heat. The latter supposition we have no analogies strong 
enough to warrant us to adopt, though were heat really not polar- 
ized by tourmaline, we must have done so. All our experiments 
point to the first, namely, that heat, though intimately partaking 
of the nature of light, and accompanying it under certain circum- 
stances (as in refraction and reflection), is capable of almost com- 
plete separation from it under others. Thus, almost all the heat 
is stopped by a plate of alum, which transmits nearly the whole 
light, whilst a second plate of tourmaline stops the whole light, 
but transmits a large share of the heat. 
26. The tourmaline affords a precious method of investigat- 
ing the influence of light, since the quantity of matter to be tra- 
versed is exactly the same, whatever be the direction of the axes 
of the crystal. In this it differs from all other modes of absorp- 
tion. 
* It appears that the axes of E and F were not precisely crossed in these ex- 
periments. 3 
