KNOBLAUCH ON HADIANT HEAT. 



42,9 



5°-l7 to 5°-42, when the direct radiation upon the pile had de- 

 flected the needle 20°. 



The following table contains the values, each the arithmetic 

 mean of three experiments, observed in the diathermanous bodies 

 mentioned, as also in others : — 



Table LII. 



after the inseTtion when the heat o{ platinum below 234° F. is reflected by 



spar causes the needle to deviate 8°'67 ; that portion reflected 

 by black paper, 7°*83 ; and that reflected by carmine, 11°'42, the 

 deflection by direct radiation as before amounting to 20°. 



The following table contains the observations which were 

 instituted on this point, in addition to those already mentioned 

 (each the arithmetic mean of three experiments) : — 



Table LIII. 



after the insertion when the heat of red-liot platinum is reflected by 



produces a deflection of 6°"08 ; that reflected by black paper, of 

 5°'l7 ; and that by carmine, of 9°*75 ; the direct radiation upon 

 the thermal pile causing a deviation of 20° in the needle of the 

 galvanometer. 



* The heat reflected by red-hot platinum has been previously (p. 401and405) 

 examined ; however, it appeared to me requisite to repeat the experiments on 

 this occasion, so as to be enabled to annex them with greater certainty to the 

 others which beloiif; here. The relation of the numbers to each other found 

 was of course the same as before, ;:Uhough their absolute values were diderent 

 from tlie former, which cannot surprise us, as lliey w?re observed almost a 

 wliole year subsequently. 



