KNOBLAUCH OX RADIANT HEAT. 



225 



the heat, to the rays of an Argand lamp (which, as before, was 

 used without the chimney) . The size of the screen which they 

 formed was sufficient to protect the direct rays of the flame from 

 the thermal pile, so that the latter was reached by those only 

 which the heated bodies themselves emitted to it through the 

 diaphragm. By withdrawing the latter or the lamp, it was easy 

 to produce the constant direct deflection of 35° in the multiplier, 

 which remained constant as soon as the screens had acquired a 

 maximum temperature C3rresponding to the conditions, the 

 proper temperature. Of course this point must be waited for, 

 before the diathermanous substances are inserted on the side of 

 the diaphragm next the pile. 



The radiating adiathermanous bodies, all of which were in 

 discs 11 centim. in diameter, Mere in general the same as in the 

 first experiments — metal, wood, porcelain, leather, cloth, &c. 

 The black paper, as also that covered by carmine, were coated 

 on one side with lamp-black. A third piece was blackened 

 on both sides. A net-work of metal was coated with white 

 lead and red Venetian lac. The transmission of the heat 

 emitted by them gave the same result as before. On this occa- 

 sion a recession of the needle from 35° to 10°-10°'33 con- 

 stantly occurred when the red glass, and from 35° to 7°'08-7°'l7 

 when the plate of calcareous spar was inserted between the 

 heated screen and the thermoscope, of whatever the former was 

 composed. 



The following table shows how perfectly the observations 

 in this series of experimcrits agree with those of the first 

 (p.223):- 



Table XV. 



