through different solid and liquid bodies. 229 



are to be entirely cut off, a plate of polished brass is interposed. 

 When the transmitting power or capacity of any substance is to be 

 tried, that substance is placed on the opening of the screen, the 

 plate of copper is removed, and in five or six seconds the needle by 

 its oscillations and final deviation, shows the ultimate effect. It is 

 remarkable that the needle acquires a stable position in a minute and 

 a half, whatever the thickness of the transparent medium through 

 which the heat passes, from one hundreth of a line to five or six 

 inches. The constancy of this interval of time, under such varied 

 thicknesses, proves unquestionably that the heat which falls on the 

 pile is exclusively that which passes immediately through the inter- 

 posed substance. 



Thus it is proved incontestably, that rays of heat are immediately 

 transmitted through solid and liquid bodies, possessed of a certain 

 degree of transparency. But is the amount of heat thus transmitted 

 in proportion to the transparency ? This is the question which the 

 experiments of the author appear to have solved. 



The following tables give the indications of the galvanometer for 

 different substances, reduced to the same thickness. They were ob- 

 tained under circumstances the most favorable to the identity of the 

 laws of transmission for heat and light, — for the radiating source be- 

 ing a lamp with a double current of air, there was at the same time 

 a very abundant transmission of both of these agents. The number 

 of rays transmitted, was calculated by dividing the galvanometric 

 force, by the total force when the rays fall directly on the pile. The 

 numbers are expressed in hundredths of the quantity of incident 

 heat. 



TABLE I. 



Liquids. (Common thicknes 9.21""".) 

 Open screen, _ - _ _ _ 



Carburet of sulphur, (colorless,) 

 Chloride of sulphur, (deep red brown,) 

 Protochloride of phosphorus, (colorless,) 

 Hydrocarburet of chlorine, (colorless,) - 

 Oil of nuts, (yellow,) - _ . - 



Essence of turpentine, (colorless,) - 



" rosemary, (colorless,) 

 Oil of colza, (yellow,) - - . 

 Oil of olive, (greenish yellow,) 

 Balsom ofcopaiva, (pretty deep yellow brown,) 

 Essence of lavender, (colorless,) 



