366 Mr. 8. C. Laws on the Thomson Effect 
conductor in which there is a gradient of temperature, de 
“zs ce 
then 
HH, =Cyo = enes 
where C is measured in electromagnetic 
units and ¢ is the specific heat of electricity, 
or Hos - o - ergs, 
where ©, is expressed in amperes. 
Also if H, is the quantity of heat evolved per unit length 
per unit time by a current C,, then, by Joule’s law, 
H,=C,’r ergs, where r is the resistance per unit length, 
and both C, and 7 are measured in C.G.S. electro- 
magnetic units, 
or H,=10'xC,?. 7, where C, and +» are expressed in 
amperes and ohms respectively. 
Hence if 6,, 6, be the changes in the compensating currents 
in the two cases, these are proportional to the corresponding 
changes of temperature, and 
C dO. 
Bt! 18a es ae Bae 
H,! S52") Wey TOS 
Or <_ LON GTO Cas am 
; OT Ae Reel flare shel Be 
ergs per U.G.S. absolute unit current per 1° C. 
The validity of the above assumption that the amount of 
heat produced is proportional to the change of temperature is 
evident from the following data obtained for the rise of 
temperature due to different currents in the rods—1*Z3 per 
cent. tin. 





Current in rods , Compensating current x 
C,. We ee 
| | zoe 
1:5 amperes. | 9°97 4°43 
16 i | ti") 4:34 
. 
30 a | 39°6 4°40 | 
It will be seen that within the limits of error of experiment, 
the rise in temperature is proportional to the square of the 
current, or, by Joule’s law, to the amount of heat developed. 
