98 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XII.) 



dition, and employed in sustaining the inductive action, and consequently the tension 

 belonging- to the smaller number on which the limited force was originally accumu- 

 lated, must fall in a proportionate degree. 



1373. For the same reason diminishing these opposing surfaces must increase the 

 intensity up to the condition even of their becoming points. But in this case, the ten- 

 sion of the particles of the dielectric next the points is higher than that of particles 

 midway, because of the lateral action and consequent bulging, as it were, of the lines 

 of inductive force at the middle distance (1369.). 



1374. The more exalted effects of induction on a point p, or any small surface, as 

 the rounded end of a rod, opposed to a large surface, as that of a ball or plate, than 

 when it is opposed to another point or end at the same distance, falls into harmonious 

 relation (1302.). For in the latter case, the small surface p is affected only by those 

 particles which are brought into the inductive condition by the equally small surface 

 of the opposed conductor, whereas when that is a ball or plate the lines of inductive 

 force from the latter are concentrated, as it were, upon the end p. Now though the 

 molecules of the dielectric against the large surface may have a much lower state of 

 tension than those against the similar smaller surface, yet they are also far more 

 numerous, and, as the lines of inductive force converge towards a point, are able to 

 communicate to the particles contained in any cross section (1369.) nearer the small 

 surface an amount of tension equal to their own, and consequently much higher for 

 each individual particle ; so that, at the surface of the smaller conductor, the tension 

 of a particle rises much, and if that conductor were to terminate in a point, the ten- 

 sion would rise to an infinite degree, except that it is limited, as before (1368.), by 

 discharge. The nature of the discharge from small surfaces and points under induc- 

 tion will be resumed hereafter (1425. &c.). 



1375. Rarefaction of the air does not alter the intensity of inductive action (1284. 

 1287.) ; nor is there any reason, as far as I can perceive, why it should. If the quan- 

 tity of electricity and the distance remain the same, and the air be rarefied one half, 

 then, though one half of the particles of the dielectric are removed, the other half 

 assume a double degree of tension in their polarity, and therefore the inductive forces 

 are balanced, and the result remains unaltered as long as the induction and insulation 

 are sustained. But the case of discharge is very different ; for as there are only half 

 the number of dielectric particles in the rarefied atmosphere, so these are brought 

 up to the discharging intensity by half the former quantity of electricity ; discharge, 

 therefore, ensues, and such a consequence of the theory is in perfect accordance 

 with Mr. Harris's results (1365.). 



1376. The increase of electricity required to cause discharge over the same di- 

 stance, when the pressure of the air or its density is increased, flows in a similar man- 

 ner, and on the same principle, from the molecular theory. 



1377- Here I think my view of induction has a decided advantage over others, espe- 

 cially over that which refers the retention of electricity on the surface of conductors 



