SCT.XXV. MELLONI'S EXPERIMENTS. 211 



the temperature of 178^ of Fahrenheit. Rock-salt 

 transmitted heat in the proportion of 92 rays out of 

 100 from each of these sources; but all other sub- 

 stances pervious to radiant heat, whether solid or 

 liquid, transmitted more caloric from sources of high 

 temperature than from such as are low. For instance, 

 limpid and colorless fluate of lime transmitted in the pro- 

 portion of 78 rays out of 100 from the lamp, 69 from 

 the platiua, 42 from the copper, and 33 from the hot 

 water; while transparent rock-crystal transmitted 38 

 rays in 100 from the lamp. 28 from the platina, 6 

 from the copper, and 9 from the hot water. Pure ice 

 transmitted only in the proportion of 6 rays in tbte 100 

 from the lamp, and entirely excluded those from the 

 other three sources. Out of 39 different substances, 

 34 were pervious to the calorific rays from hot water, 

 14 excluded those from the hot copper, and 4 did not 

 transmit those from the platina. 



Thus it appears that heat proceeding from these 

 sources is of different kinds : this difference in 

 ture of the calorific rays is also proved by another, 

 periment, which will be more easily understood from 

 the analogy of light. Red light emanating from red 

 glass, will pass in abundance through another piece of 

 red glass, but it will be absorbed by green glass : green 

 rays will more readily pass through a green medium 

 than through one of any other color. This holds with 

 regard to all colors; so in heat. Rays of caloric of the 

 same intensity, which have passed through different 

 substances, are transmitted in different quantities by the 

 same piece of alum, and are sometimes stopped alto- 

 gether ; showing that rays which emanate from different 

 substances possess different qualities. It appears that 

 a bright flame furnishes rays of heat of all kinds, in the 

 same manner as it gives light of all colors ; and as col- 

 ored media transmit some colored rays and absorb the 

 rest, so bodies transmit some ray of caloric and ex- 

 clude the others. Rock-salt alone resembles colorless 

 transparent media in transmitting all kinds of caloric, 

 even the heat of the hand, just as they transmit white 

 light, consisting of rays of all colors. 



The property of transmitting the calorific rays di- 



ese tour 

 th im- 

 :h..-r ex- 



