46 Dr. Hare's Letter to Prof. Faraday 



fection will be inversely as their number as alleged by you. 

 No such law holds good in the communication of heat. The 

 air in contact with a surface at a constant elevation of tem- 

 perature, such for instance as might be supported by boiling 

 water, would not become hotter by being rarefied, and conse- 

 quently could not become more efficacious in the conduction of 

 heat from the heated surface to a colder one in its vicinity. 



7. As soon as I commenced the perusal of your researches 

 on this subject, it occurred to me that the passage of electricity 

 through a vacuum, or a highly rarefied medium, as demon- 

 strated by various experiments, and especially those of Dav}', 

 was inconsistent with the idea that ponderable matter could 

 be a necessary agent in the process of electrical induction. 

 I therefore inferred that your efforts would be primarily di- 

 rected to a re-examination of that question. 



8. If induction, in acting through a vacuum, be propagated 

 in right lines, may not the curvilinear direction which it pur- 

 sues, when passing through " dielectrics," be ascribed to the 

 modifying influence which they exert? 



9. If, as you concede, electrified particles on opposite sides 

 of a vacuum can act upon each other, wherefore is the received 

 theory of the mode in which the excited surface of a Leyden 

 jar induces in the opposite surface a contrary state, objec- 

 tionable ? 



10. As the theory which you have proposed, gives great 

 importance to the idea of polarity, I regret that you have not 

 defined the meaning which you attach to this word. As you 

 designate that to which you refer, as a " species of polarity," 

 it is presumable that you have conceived of several kinds with 

 which ponderable atoms may be endowed. I find it difficult to 

 conceive of any kind which maybe capable of as many degrees 

 of intensity as the known phaenoinena of electricity require ; 

 especially according to your opinion that the only difference 

 between the fluid evolved by galvanic apparatus and that 

 evolved by friction, is due to opposite extremes in quantity and 

 intensity ; the intensity of electrical excitement producible by 

 the one being almost infinitely greater than that which can be 

 produced by the other. What state of the poles can consti- 

 tute quantity — what other state intensity, the same matter be- 

 ing capable of either electricity, as is well known to be the 

 fact? Would it not be well to consider how, consistently 

 with any conceivable polarization, and without the assistance 

 of some imponderable matter, any great difference of intensity 

 in inductive power can be created ? 



11. When by friction the surface is polarized so that par- 

 ticles are brought into a state of constraint from which they 



