ELECTRICITY. 



of about half an inch in diameter, and 

 arrange the wires of the discharger with 

 their points in ths direction of the groove, 

 and at four inches from each other, the 

 ball being equally distant from each. On 

 passing a small charge from one wire to 

 the other, the ball will be driven from 

 the positive to the negative wire, and this 

 effect will be constant if the wires ter- 

 minate in points ; but if they are knob - 

 bed, the ball frequently vibrates between 

 them, because the influence of the at- 

 tracting surfaces upon the ball interferes 

 with the regularity of the effect, and often 

 renders the result equivocal. 



(226.) The nature and place of the 

 perforation effected in a card by the 

 passage of an electric charge, of which 

 we have already given an account ( 159), 

 appear to favour the same view of the 

 subject. The following experiment, also, 

 shews that the impulse is communicated 

 most forcibly in the direction from the 

 positive towards the negative conductor. 

 A light float-wheel, the vanes of which 

 are mads of card paper, inserted in the 

 circumference of a cork turning freely 

 on a pin passed through its centre as an 

 axle, will be put in motion by presenting 

 to it an electrified point, apparently in 

 consequence of the impulse of the stream 

 of air which issues from the point. 

 Whether the point be positively or nega- 

 tively electrified, the direction of the 

 motion, as well as of the stream of air, is 

 always the same. But if the wheel be 

 placed on an insulating stem, as in fig. 

 42, and introduced between the pointed 

 Fig. 42. 



wires of the universal discharger, which 

 are to be placed as accurately as possible 

 opposite to each other, and at the distance 

 of an inch or more from the upper vanes ; 

 on connecting one of the wires with the 

 positive, and the other with the negative 

 conductor of an electrical machine, and 

 exciting it, the wheel will move as if im- 

 pelled by a stream from the positive to 

 the negative wire. On reversing the 

 connections, so that the electricity of 

 each wire is changed, the motion of the 

 wheel will likewise be reversed. 



(227.) If a card be placed vertically, 

 by inserting it in a small piece of cork 

 that may form a base of about a quarter 



of an inch wide for it to stand upon, but 

 so lhat it may be overthrown by the 

 smallest impulse ; and the pointed wires 

 of the universal discharger be brought 

 opposite to each other, and about a 

 quarter of an inch below the upper edge 

 of the card, which stands at an equal 

 distance between them ; on connecting 

 the wires with a machine, or with an in- 

 sulated jar, so as to effect an electric 

 discharge between them, the card will 

 be thrown down, and will constantly 

 fall from the positive, and towards the 

 negative wire. 



(228.) The determination of a stream 

 of electrified air in this direction is also 

 rendered very sensible by the motions of 

 smoke or vapour placed in the circuit 

 of the electricity. Thus the flame of a 

 taper placed between two oppositely 

 electrified balls will constantly be blown 

 from the positive to the negative side. 

 Fig. 43 represents two hollow metallic 



Fig. 43. 



balls, about three quarters of an inch in 

 diameter, insulated on separate glass 

 pillars, by which they are supported at 

 a distance of two inches from each other : 

 the upper part of each ball is hollowed 

 into a cup, into which a small piece of 

 phosphorus is to be put. A small candle 

 has its flame situated mid-way between 

 the balls, one of which is connected with 

 the positive, and the other with the nega- 

 tive conductor of the machine. When 

 the balls are electrified, the flame is 

 agitated, and inclining towards the one 

 which is negative, soon heats it suffi- 

 ciently to set fire to the phosphorus it 

 contains, whilst the positive ball remains 

 perfectly cold, and its phosphorus un- 

 melted. On reversing the connections 

 of the balls with the machine, the phos- 

 phorus in the other ball will now be 

 heated and will inflame. 



(229.) However plausibly it may have 

 been inferred, from a superficial view 

 of these facts and experiments, that the 

 electric fluid actually possesses momen- 

 tum, and that it moves in a particular 

 direction, a more rigid analysis of the 

 phenomena will show that they in no 



