towards the Theory of Thermo-electricity. 211 



the same order as in thermo-electricity, is that of radiation ; 

 and therefore he supposes that two pieces of hot metal, in 

 contact, radiate in the same proportions as they would if se- 

 parate and exposed ; and that thermo-electricity is a result of 

 this inter-radiation. 



This is certainly applying to the term radiation a new 

 meaning, very little analogous to its ordinary acceptation*. Yet 

 the same quality, whatever it may be, which occasions radiation 

 to be more or less copious, may also determine a superficial com- 

 munication, proportionately copious, though different in mode. 

 We have evidence, too, that the superficial absorbent power 

 for heat, is proportionate to the radiating power; and it seemed 

 not very improbable that here might be found some trace 

 towards the solution of the problem. 



9. If the effects were due. to any cause connected with, or 

 related to radiation, they should be modified by alterations in 

 the surfaces ; and by making the surfaces of a thermo-electric 

 pair identical, their reaction should be greatly weakened, if 

 not neutralized altogether. 



An iron and a copper wire, of the same size (10 x T ^ inch), 

 were well tinned from end to end, and twisted together for an 

 inch. A similar pair, untinned, but polished, were similarly 

 joined ; and the feet tinned for \ an inch, that the contacts 

 with the mercury might be alike. Instead of the tinned wires 

 having their efficacy impaired, they gave greater deflections 

 than the clear ones. This unexpected fact, verified in a 

 great number of ways, led to a long course of experiments; 

 the general bearings of which will occupy a subsequent sec- 

 tion (VIII.). 



I am at a loss to reconcile with this fact any cause con- 

 nected with radiation. 



10. To try radiation more directly, and on a larger scale, 

 a plate of tinned iron was wired round with tinned iron wire, 

 which projected at one corner, for a conductor. A sheet of 

 soft tin was also wired round with copper wire, projecting in 

 the same manner, and for the same purpose. The sheet tin 

 being laid on the tin plate, with a leaf of bank post paper 

 between, to prevent contact, the conductors were plunged 

 into the mercury of the magnetest, and a couple of lamps 

 placed under the tin plate. The whole soon became hot, 

 without deflecting the needle. The tin sheet was now lifted 

 off, the paper removed, and a few threads spread about the 



* [It appears to us, on the contrary, that M. Becquerel here uses the term 

 radiation in a sense perfectly similar to its ordinary acceptation : see Sir J. 

 Herschel's remarks on the process by which radiation and conduction slide 

 into each other, in his Prel. Disc, on Nat. Phil.— Edit. ] 



2 E2 



