tances.” Agreeably to the former, you conceive that ‘* assuming 
_ that a perfect vacnum was to intervene in the course of the line 
2 A letter to Prof. Faraday. 
of being an action of either particles or masses at “ sensible dis- — 
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. E 
should act at a distance of half an inch on all the particles — : 
the disk of the inner superficies of the bounding sphere.” 
Laying these quotations before you for reconsideration, I bog 4 
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 — 
Pek te Mia aig ie aad Eb 
£ 
< 
_ Masses at sensible distances,” how can a particle situated as above 
_ described, “act at the distance of half an inch on all the — 
PS forming the disk of the inner superficies of the bounding sphere?” 
* 
+ ae 
ed 
e = 
a 
its vicinity. 
What i is a sensible distance, if half an inch is not? 4 
.. How can the force thus exercised obey the “well known law i 
‘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 pean be- 
come more remote ? ‘ 
~ Can the ponderable particles of a gas be deemed contiguous in 
_the true sense of this word, under any circumstances? A it : 
may be well here to observe, that admitting induction to arise from 
an affection of intervening ponderable atoms, it is difficult to com — 
ceive that the intensity of this affection will be inversely as the 
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 
supported by boiling water, would not become hotter by beiNg — 
rarefied, and consequently could not become more efficacious i 
the conduction of heat from the heated surface to a colder one in 
As soon as I commenced the perusal of your researches on this nl 
subject, it occurred to me that the passage of electricity throug 
a vacuum, or a highly rarefied medium, as demonstrated by val 
