Dimensions of a Body on its Thermal Emission. ''Ill 



The ratio of the thermoelectric E.M.F.'s is approximately 

 the same as the ratio of the excess temperatures of the points 



Fisr. 2. 



WATER OUTLET 



STEAM IN LET 



STEAM , 

 EXIT 



BRASS ROD 



GALVANOMETER 



•rTTTTTTinrrTrrirtf^v 

 100 OHMS--* 



SECONDARY CELL 



A and B after it has been corrected for slight differences of 

 temperature between the two water-batbs and the water- 

 jacket. Two jackets have been employed so far, and com- 

 pared with each other and with the bar unjacketed. In this 

 last case the bar is merely shielded from the ruder form of 

 draught by brown-paper screens. 



The results are given in the subjoined table : — 



E. 



Inner radius 



of enclosure 



in centim. 



Indefinitely 

 great. 



515 

 1-6 



Excess 

 tempera- 

 ture of A. 

 A . 



540 

 57-0 

 611 



Excess 

 tempera- 

 ture of B. 

 0„. 



30-5 

 33-3 

 3(5-6 



Average 

 excess. 



42-2 

 453 



48-8 



Emissivity 

 at stated 

 mean ex- 

 cess tem- 

 perature. 



•0001882 

 •0001610 

 •0001514 



Emissivity 

 approximately 

 corrected to 

 one tempera- 

 ture. 



•000191 

 •000162 

 •000151 



The values of emissivity here given have been calculated 

 from the formula = ^ r logfl A -l gfl B n| 



' 2 |_ -4343 x x J ' 

 Phil. Mag. S 5. Vol. 39. Nq. 238. March 1895. U 



