*2~)§ Influence of Radiation on the Transmission of Heat. 



which in the above investigation has been denoted by k. is 

 round to be 



Here k represents the coefficient of absorption of the normal 

 rays. As long as the radiation at any point of a solid is 

 equal or nearly equal to the internal radiation of a body at 

 uniform temperature, the previous results are correct there- 

 fore, provided we take k to be equal to twice the coefficient 

 of absorption of the normally incident rays. But the absorp- 

 tion of the body itself will tend to diminish the intensities of 

 the oblique radiation, and though this diminution is partly 

 made up by the radiation of the absorbing layer, the tendency 

 on the whole will be that the normal radiations will increase 

 relatively in intensity. The effect will be that /c will gradually 

 diminish from its original value to half its amount. As the 

 purpose of our calculation was not the exact numerical calcu- 

 lation of the effects of radiation, but rather the study of its 

 general influence and the determination of the order of mag- 

 nitude of the effects, the results looked upon in this light will 

 not be affected by the assumption made. The same will 

 apply to the neglect of the dependence of radiation on wave- 

 length. This simplification will introduce an error the character 

 of which will be of the same nature as that just discussed, so 

 that the apparent coefficient of absorption will gradually 

 diminish, only those radiations traversing an appreciable 

 thickness of the plate which are not strongly absorbed by it. 

 As a matter of experiment it has, however, been found that 

 by a proper adjustment of the constant a;, the total radiation 

 traversing a thickness t of a plate diminishes as e~ K \ with a 

 near approach to accuracy, which justifies the equation on 

 which our calculations are based. While it is well to draw 

 attention to the approximate nature of the results, in so far as 

 they depend on the assumptions made, the nature of the 

 influence of radiation in the transmission of heat is sufficientlv 

 well represented by the equations which have been obtained. 

 It will be the object of a further communication to .studv 

 effects of radiation on the temperature distribution in large 

 masses of gas in a state of convective equilibrium. 



Description of Plate II. 



The curves represent the temperature variation within a plate 

 5 cm. thick, the' surfaces being kept at a difference of 1°, the 

 ordinates representing temperatures, aud the abscissae distances 

 across the plate. The material of the plate is supposed to have a 



