106 g Dr. C. V. Burton on a 



63. Within the substance o£ the slab there is at each 

 instant a quasi-electromotive intensity T and a true electro- 

 motive intensity — 47rV 2 ?, V being the velocity of radiation. 

 For simplicity it will now be supposed that the only opposing 

 forces are due to electrical resistance; thus in the absence of 

 appreciable inertia effects, the relation 



(T-±TrY*<:)c = d<:/dt . . , . . (76) 



is always satisfied ; c being the conductivity of the substance 

 of the slab. Using (74) and (75), 



9o = T c/(47rY 2 c + ; S ). ..... (77) 



This gives for the current-density 



I = ^° e = WyV4/ V ; • • (78) 



or, separating the real from the imaginary problem, we have, 

 corresponding to 



T = T cos^, (79) 



I= l6?W (5C0S ^ 47rV2csin4, * (80) 



64.^The rate, in ergs per second, at which energy is being 

 dissipated as heat in each cubic centimetre of the conductor 

 is accordingly 



-= i« n^L 2 (^os^-47rV^sin,0 2 ; • (81) 



c lb7rW + ^ 



so that 



„ I 2 1 T cs ,^ 9 x 



average of 7 = 2l67r 2 W + . 2, ' * * {b2) 



The last-written expression is a maximum with respect to c 

 when c = s/47rV 2 , in which case the average of I 2 /c becomes 



T 2 s/167rV 2 ' . . (83) 



64. Eemembering (73), we find that, with the particular 

 set of numerical values adopted in the foregoing table 

 T = 130 volts per cm., or in absolute e.m. units l*3xl0 10 ; 

 s=27rn = 27rx 1*29 X 10 10 ; the average rate at which energy 

 is being dissipated in the conductor being in that case 



3 x 10 8 ergs per sec. per ex. or about 7*5 calories per sec. per c.c. 



This is with the conductivity most favourable to dissipation, 



