2 A letter to Prof. Faraday. 



of being an action of either particles or masses at ^^ sensible dis- 

 tances.^'' Agreeably to the former, you conceive that "assuming 

 that a perfect vacuum was to intervene in the course of the line 

 of inductive action, it does not follow from this theory that the 

 line of particles on opposite sides of such a vacuum would not act 

 upon each other." Again, supposing "it possible for a positively 

 electrified particle to be in the centre of a vacuum an inch in di- 

 ameter, nothing in my present view forbids that the particle 

 should act at a distance of half an inch on all the particles forming 

 the disk of the inner superficies of the bounding sphere." 



Laying these quotations before you for reconsideration, I beg 

 leave to inquire how a positively excited particle, situated as above 

 described, can react " inductrically" with any particles in the super- 

 ficies of the surrounding sphere, if this species of reaction require 

 that the particles between which it takes place be contiguous. 

 Moreover if induction be not "an action either of particles or 

 masses at sensible distances," how can a particle situated as above 

 described, "ac^ at the distance of half an inch on all the particles 

 formdng the disk of the inner superficies of the bounding sphere ?" 

 What is a sensible distance, if half an inch is not? 



How can the force thus exercised obey the " well known law 

 of the squares of the distances," if as you state (1375) the rare- 

 faction of the air does not alter the intensity of the inductive ac- 

 tion ? In proportion as the air is rarefied, do not its particles be- 

 come more remote ? 



Can the ponderable particles of a gas be deemed contiguous in 

 the true sense of this word, under any circumstances ? And it 

 may be well here to observe, that admitting induction to arise from 

 an affection of intervening ponderable atoms, it is difficult to con- 

 ceive that the intensity of this affection will be inversely as their 

 number as alleged by you. No such law holds good in the com- 

 munication of heat. The air in contact with a surface at a con- 

 stant elevation of temperature, such for instance as might be 

 supported by boiling water, would not become hotter by being 

 rarefied, and consequently could not become more efficacious in 

 the conduction of heat from the heated surface to a colder one in 

 its vicinity. 



As soon as 1 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 demonstrated by vari- 



