8 Second Letter from Dr. Hare to Prof. Faraday. 



Ill paragraph (xxv,) you allege that conduction of heat differs 

 from electrical induction, because it passes by a very slow pro- 

 cess; while induction is in its distant influence simultaneous 

 with its force at the place of action. How then can the passage 

 of heat by conduction, be '^ a process precisely like that of radia- 

 tion,'^ (xxi,) which resembles induction in the velocity with which 

 its influence reaches objects, however remote ? 



Although, (xxi,) you appeal to the " modern views respect- 

 ing radiation and conduction of heat," in order to illustrate your 

 conception of the contiguity of the particles of bodies subjected 

 to induction, yet in (xxv,) you object to the reference which I had 

 made to these views, in order to shew that the intensity of elec- 

 tropolarization could not be inversely as the number of particles 

 interposed between the " inductric" surfaces. Let us then resort 

 to that above suggested, of the influence of the poles of a mag- 

 net upon intervening pieces of iron wire. In 1679, 14th series, 

 you suggest this as an analogous case to that of the process of 

 ordinary electrical induction, which we have under consideration. 

 Should there be in the one case a thousand pieces of wire inter- 

 posed, in the second an hundred, will it be pretended that the in- 

 tensity of their reciprocal inductive reaction would be inversely 

 as the number; so that the effect of the last mentioned number 

 of wires would be equivalent to that of the first ? Were inter- 

 vals to be created between the wires by removing, from among 

 the number first mentioned, alternate wires, it would seem to me 

 that the diminution of effect would be commensurate not only 

 with the reduction of the number of the wires, but likewise with 

 the consequent enlargement of the intervals. 



any excess of this principle with which a feeble affinity may have caused them to 

 be transiently united, or in receiving the rays emitted by any heated body, to the 

 emanations from which they may have been exposed. 



" We may account, in like manner, for the great radiating power of earthen ware 

 and wood. 



" For the same reason that calorific rays cannot be projected from the interior of a 

 metal, they cannot enter it when projected against it from without. On the contra- 

 ry, they are repelled with such force as to be reflected without any perceptible 

 diminution of velocity. Hence the pre-eminence of metallic reflectors. 



" It would seem as if the calorific particles which are condensed between those of 

 the metal, repel any other particles of their own nature wliich may radiate towards 

 the metallic superficies, before actual contact ensues ; otherwise, on account of me- 

 chanical imperfections, easily discernible with the aid of a microscope, mirrors 

 would not be as efficacious as they are found to be in concentrating radiant heat. 

 Their influence, in this respect, seems to result from the excellence of their gen- 

 eral contour, and is not proportionably impaired by blemishes." 



