AUB MECHANICAL CONDITION ON EADIANT HEAT. 91 



Table II. (continued). 



Substance. Kadiation. 



Iodide of Lead 36-0 



Sulphide of Mercury .... 30-6 



Spongy Platinum 31-5 



Washed Sulphur (flowers) . . 32*3 



Sulphide of Zinc . . , . 36-1 



Amorphous Phosphorus . . . 38'0 



Chloride of Lead 39-0 



Chloride of Cadmium .... 40-0 



Fluor-spar 48-6 



Sulphide of Calcium .... 49'1 



Sulphate of Baryta 51 '3 



Sugar 52-1 



Red oxide of Lead 56'5 



Sulphide of Cadmium . . . . 56"9 



Sulphate of Lime . . . . . 59-3 



Chloride of Silver (black) . . . 60-0 



Carbonate of Zinc 62*0 



Oxide of Cobalt 62-5 



Iodide of Copper 63*0 



Eed oxide of Iron 63*8 



Sulphide of Iron . . . . 65 "6 



Black oxide of Iron . . . . 65 '8 



The agreement as regards relative radiative power between this and the former Table 

 is as good as could under the circumstances be expected. The experiments have been 

 several times repeated, and the .Table contains the means of results which were never 

 widely different from each other. 



The quantity of radiant heat emitted by bodies in all states of aggregation having 

 been thus conclusively shown to depend mainly upon its molecular character, the 

 question as to the quality of the heat emitted next arises. In examining this point, I 

 contented myself with testing the heat by its transmission through rock-salt. The 

 choice of this substance involved the solution of the still disputed question whether 

 rock-salt is equally pervious to all kinds of rays *. For if it absorbed the radiation from 

 two different bodies in different degrees, it would not only show a difference of quality 

 in the radiations, but also demonstrate its own incapacity to transmit equally rays of all 

 descriptions. 



* The last publication on this subject is from the pen of that extremely able experimenter, Professor 

 Knoblauch. After discussing the results of De la Provostate and Desains, and of Mr. Balfotje Stewaet, he 

 arrives at a different conclusion, namely, that pure rock-salt is equally pervious to aU kinds of heat. — Pogg. 

 Ann. 1863, vol. cxx. p. 177. 



o2 



