102 Observations on Mr. Donovaii's Reflecimts, &c. 



vial possesses (nearly) the same quantity of electric Jluid, both 

 when it is in its natural stale, and when it is charged ; hut the 

 electric Jiiiii I is not distributed in the same manner in both cases. 

 When an electric machine tends to produce an accumulation of 

 electric fiuid on one of the surfaces of the vial, it cannot accu- 

 mulate except the outside of the vial can part with an equal 

 quantity, its coating being in communication with the ground. 

 But it is not the identical electric fluid which pervades the glass, 

 the electric 7Jiafter thrown in remains fixed on the inner surlace; 

 the defereJit fluid alone pei'vades the glass, and, uniting with the 

 electric matter on the outward surface, forms there an ecjual 

 quantity of electricfluid, which is transmitted to the ground if 

 it finds a conductor. This is a complete analogy with one of 

 the phaenomena of the aqueous vapour mentivued in the above 

 quoted stclion. The maximum of charge is attained, when the 

 quantity of electric matter accumulated on the internal surface 

 is in equilibrium with that transmitted by the electric machine. 



23. So far this system might appear only an hypothesis to 

 Mr. Donovan, as he does not know the work to wliich I refer, 

 where I have given a peremptory demonstration of it, derived 

 from the electric moliovs, proving by a direct experiment, that 

 these motions refer only to the electric matter, without inter- 

 ference of the deferent fluid, except to transport the electric 

 matter. 



24. In tome ii. p. 8, I have related an experiment which 

 very much struck Mr. Cavallo, in presence of whom I made it at 

 Windsor. The apparatus for that experiment is described, with 

 a plate, in my work ; it consists of a conductor supported in an 

 horizontal position on an insulating pillar. At one end of this 

 conductor are suspended, by brass vvire, two cork-balls half an 

 inch diameter going down so as to hang opposite to the centre of 

 two insulated brass disks two inches diameter, brought to about 

 oy inches of each other^ and the balls hung at equal distance 

 irom them. I give a spark to each of the disks with a Leyden 

 rial : the deferetil fluid of the disksj thus rendered positive, and 

 giving more expansive power to the fluid of the balls, a part of 

 it is carried towards the other extremity of the insulated con- 

 ductor; and the balls losing thus a part of their electric matter, 

 they diverge as being in a negative state, and are carried on both 

 sides towards the positive disks, which they would strike, were 

 they not prevented by a kind of bridle, placed at the end of the 

 conductor, showing by small motions as it were an avidity to 

 move towards them. 



25. In that staf; of the apparatus in which the influence of 

 the disks, being pwi/ii'f'; gives more e>:pan&ive power to the elec- 



• . ■ , . trie 



