RELATION OF A VACUUM TO ELECTRICAL PHENOMENA. 155 



luminous discharge to be principally on the inner surface of the glass ; and it does 

 not appear at all unlikely, that, if the vacuum refused to conduct, still the surface of 

 glass next it might carry on that action. 



1614. At one time, when I thought inductive force was exerted in right lines, I 

 hoped to illustrate this important question by making experiments on induction 

 with metallic miiTors (used only as conducting vessels) exposed towards a very clear 

 sky at night time, and of such concavity that nothing but the firmament could be 

 visible from the lowest part of the concave n, fig. 29. Such mirrors, when electrified, 

 as by connection with aLeyden jar, and examined by a carrier ball, readily gave elec- 

 tricity at the lowest part of their concavity if in a room ; but I was in hopes of finding 

 that, circumstanced as before stated, they would give little or none at the same spot, 

 if the atmosphere above really terminated in a vacuum. I was disappointed in the 

 conclusion, for I obtained as much electricity there as before ; but on discovering 

 the action of induction in curved lines (1231.), found a full and satisfactory explana- 

 tion of the result. 



1615. My theory, as far as I have ventured it, does not pretend to decide upon the 

 consequences of a vacuum. It is not at present limited sufficiently, or rendered pre- 

 cise enough, either by experiments relating to spaces void of matter, or those of other 

 kinds, to indicate what would happen in the vacuum case. I have only as yet en- 

 deavoured to establish, what all the facts seem to prove, that when electrical phe- 

 nomena, as those of induction, conduction, insulation and discharge occur, they de- 

 pend on, and are produced by the action of contiguous particles of matter, the next 

 existing particle being considered as the contiguous one ; and I have further assumed, 

 that these particles are polarized ; that each exhibits the two forces, or the force in 

 two directions (1295. 1298.) ; and that they act at a distance only by acting on the 

 contiguous and intermediate particles. 



1616. But assuming that a perfect vacuum were to intervene in the course of the 

 lines of inductive action (1304.), it does not follow from this theory, that the particles 

 on opposite sides of such a vacuum could not act on each other. Suppose it possible 

 for a positively electrified particle to be in the centre of a vacuum an inch in diameter, 

 nothing in my present views forbids that the particle should act at the distance of half 

 an inch on all the particles forming the inner superficies of the bounding sphere, and 

 with a force consistent with the well-known law of the squares of the distance. But 

 suppose the sphere of an inch were full of insulating matter, the electrified particle 

 would not then, according to my notion, act directly on the distant particles, but on 

 those in immediate association with it, employing all its power in polarizing them ; 

 producing in them negative force equal in amount to its own positive force and directed 

 towards the latter, and positive force of equal amount directed outwards and acting 

 in the same manner upon the layer of particles next in succession. So that ultimately, 

 those particles in the surface of a sphere of half an inch radius, which were acted on 

 directly when that sphere was a vacuum, will now be acted on indirectly as respects 



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