230 



KNOBLAUCH ON RADIANT HEAT. 



Table XVI IL (continued). 



A constant deviation of the needle of from 9°'85 to 10°"22 is 

 now obtained on inserting the red glass, and of from 7° to 7°'25 

 on introducing the calcareous spar, be the screen of whatever 

 substance it may, provided that the direct radiation of the heat 

 emitted by it and that permeating it has produced a deflection 

 of 35°. The same applies to blue glass, alum, rock salt and 

 gypsum. All these different values, however, as far as they are 

 related, merely vary within the errors of observation. 



The same result is obtained on heating the above diatherma- 

 nous bodies by conduction to a temperature below or at 212°, by 

 placing them upon a metallic cube heated to this temperature by 

 boiling water. 



The numbers found accurately agree in this, as in the previous 

 case, with those which were formerly obtained for diathermanous 

 substances (compare Tables XIIL, XIV., XV. and XVI.). To 

 illustrate the comparison, we have annexed one of them in the 

 following table (it contains the arithmetic means of every three 

 experiments) : — 



Table XIX. 



