Physics and Chemistry. 107 
(8.) Fluorspar almost completely absorbs pure rock salt heat. 
We ought therefore to expect that the heat which it radiates 
1s more than three times greater than that from rock salt, this 
phenomenon may be explained, but the subject requires further 
investigation. 
at 150° C. rays of but one or but few wave lengths makes it possi- 
ble to institute experiments on the reflection of non-metallic sur- 
aces. The results of experiments have distinctly shown that such 
surfaces reflect different kinds of heat, or heat rays of different 
Wave lengths, in very different degrees, remarkable illustration 
is furnished by fluorspar. Of the heat radiated by different sub- 
Stances and received at an angle of 45°, quantities differing but 
little in amount are reflected by the following bodies: 
Silver, from 83 to 90 _ per cent. 
s, + -tteld- - 
Rocksalt, “f 5 to 12 e: 
luorspar, 6 to 10 wg 
greatest variety of colors without any sensible heating of 
i, 174 . 
__ the objects themselves—Pogg. Ann., exxxviti, 174. W. G 
