KNOBLAUCH ON KADIANT HEAT. 



223 



Thus a deflection of 7°*17 was observed each time a plate of cal- 

 careous spar 3*7 millim. in thickness was substituted for the red 

 glass, whether the direct radiation which deflected the needle to 

 35° was produced by heated metal, Avood, porcelain, paper, or 

 any other substance. 



The appended table (which contains the arithmetic means in 

 every case of three observations) shows how great the agreement 

 was when the heat emitted by eleven adiathermanous substances 

 was examined by means of red and blue glass, rock salt, calca- 

 I'eous spar and gypsum : — 



Table XIII. 



Thick- 

 ness in 

 milli- 

 metres. 



Substances 

 inserted. 



Deflec- 

 tion pro 

 duced by 

 direct 

 radia- 

 tion. 



Deflection produced by the insertion of the substance 

 radiating at 212° F. 



Paste- 

 board. 



1-5 

 1-4 

 14 

 4-4 

 3-7 

 1-4 



Red glass 



Blue glass 



Alum 



Rock salt 



Calcareous spar.. 

 Sulphate of lime. 



35° 



35° 



10-25 

 9-25 

 3-92 



20-75 

 7-25 

 8-75 



Thick- 

 ness in 

 milli- 

 metres. 



Substances 

 inserted. 



Deflec- Deflection produced by the insertion of the 

 tion pro- substance radiating at 212° F. 



duced by ~ 



1-5 

 1-4 

 1-4 

 4-4 

 3-7 

 1-4 



Ked glass 



Blue glass 



Alum 



Rock salt 



Calcareous spar... 

 Sulphate of lime.. 



direct 

 radia- 



Black 



tion. P^'P^''- 



Carmine 



(thick 

 layer). 



35° 



35-= 



10-25 

 9-17 



400 



20-66 



725 



8-75 



1008 

 917 

 3-92 



20-58 

 7-17 

 8-75 



Lamp- 

 black. 



1008 

 917 

 3-83 



20-50 

 7-33 

 8-66 



White 

 lead. 



Red Ve- 



netian 



lac. 



1017 

 9-17 

 3-92 



20-66 

 7-17 

 8-75 



10-25 

 9-17 

 3-75 



20-58 

 717 



8-75 



Neither, as will be evident from the following table, could any 

 diflference be perceived in the transmission when the surface of 

 the radiating bodies was modified by being scratched, although 

 this had the most decided influence upon the quantity of heat 

 emitted : — 



