YnLTAIC ELECTRICITY. 





a butterfly Hiuiponded by a thread, and hovering continually from 

 ide t<> "io Mowers. Tho more uxual form, however, 



in that of a Htnul: ut as represented in Ki/. '' 



in in the centre terminate! in a fine point, and 



the WITCH are balanced BO an to turn upon this with M lit 



turn as \>- > the arms are suspended grotesque 



figures cut in tlio shape of boys riding on birds or horncs. Those 



figures arc inodo as light as possible, ao as to require very little 



force to move them. At the top of tho pillars A and B are brass 



\ with tin- p..-itivo end of the dry pile, and B 



with tlm 11,-pitiv.' cn.l. These knobs form, in fact, the poles of 



tin- pile, and contain, therefore, a faint charge of electricity. 



I* <.f the cros* arms, small loops or ring* of wire 



are nusp.-n.l-l l.y *ilk threads, or fixed by means of shellac in 



such a way that as they 



revolve they just touch 



nobs. 



When all tin- arrange- 

 ments aru complete, tho 

 apparatus is set in mo- 

 tion. The wiro rings at 

 the ends of two of tho 

 arms Boon touch the poles 

 of th. pile, and thus be- 

 come faintly charged with 

 their electricity. They 

 are accordingly repelled, 

 and the next pair at- 

 tracted. As they revolve, 

 however, they come near 

 the opposite poles, and 

 being charged with con- 

 trary electricities to these, 

 are attracted by them. 

 On touching, they are 

 again repelled as at first ; 

 and in this way, by a 

 series of alternate attrac- 

 tions and repulsions, the 

 motion is maintained 

 without interruption, 

 often for a space of seve- 

 ral years. 



A very delicate gold- 

 leaf electroscope has been 

 devised by Bohnenberger, 

 which acts by means of a 

 dry pile. A single gold 

 leaf is used, and it ia 

 suspended midway be- 

 tween two wires connected 

 with the poles. If now 

 any free electricity be im- 

 parted to the leaf, it will 

 at once be repelled by 

 one pole and attracted 

 by the other. One great 

 advantage of this electro- 

 scope is that by noticing 

 the pole towards which 

 the leaf inclines, we shall 

 at once learn whether the 

 charge is positive or negative, 

 electroscope wo have. 



We must not, however, be led by these experiments to the 

 conclusion that electricity is produced by contact alone. They 

 do, indeed, appear to tend to this conclusion, but a largo 

 number of experiments, conducted by tho most celebrated elec- 

 tricians, prove that in all these cases the real cause of the pro- 

 duction of electricity is cJamical action produced on the one of 

 the metals which is more easily oxidised. We may take it, 

 then, as a general law that, in all cases where electricity appears 

 to arise from the contact of different metals, the real cause is 

 chemical action affecting one of them ; and further, that no 

 chemical action occurs without the production of a certain 

 amount of electricity, even though we are often unable to prove 

 its presence owing to its being in such a minute quantity , 

 or to the difficulty of collecting it. 



This is about the most sensitive 



If we place a piece of ordinary rolled zinc in a u.ixtare of 

 sulphuric acid and water in the proj*rtion of one of th former 

 to six or seven of the latter, we shall see a number of bubbles 

 given off from the surface of the zinc. The reason of this 

 is the presence of minute quantities of iron in the zinc, which 

 causes a feeble electrical action. 



Now amalgamate the surface of line that is, give it a coat- 

 ing of mercury, or quicksilver, as it is commonly called. This 

 may be done by dipping it for a short time in diluted acid, and, 

 while wot, rubbing a few drops of mercury over it. We shall 

 find that now no effect is produced on it by immersion in tho 

 u.-i'l. It retains its silvery surface, and no babbles of gas rise 

 from it. If, however, while immersed, we touch it with a rod of 

 copper or silver, we shall observe a change. The surface of 



the zinc will apparently 

 remain unaltered, bat the 

 wiro will bo coated with 

 small babbles, streams of 

 wlii.-!i rapidly ascend to 

 tho surface of the liquid, 

 and by their peculiar 

 smell and inflammability 

 are ut once seen to con- 

 sist of hydrogen gas. If 

 we allow this action to 

 continue for a little time, 

 we shall find that, though 

 the streams of bubbles 

 arise from the surface of 

 the copper, it is itself 

 unacted upon. The zinc, 

 on the other hand, will 

 have lost weight, a por- 

 tion of it being dissolved 

 in the liquid. How, then, 

 is this ? To give a satis- 

 factory explanation we 

 must slightly vary the 

 experiment. Though we 

 brought tho metals into 

 contact in the liquid, it 

 is not necessary that this 

 should be done. The only 

 thing requisite is that 

 there should be a com- 

 plete circuit for the cur- 

 rent to pass round. We 

 may, therefore, take two 

 strips of copper and zinc, 

 and placing them toge- 

 ther in the form of an 

 inverted V, make them, 

 touch outside the liquid, 

 as in Fig. 4. The bub- 

 bles of gas will, as before, 

 rise from the surface of 

 the copper. 



The best plan, however, 

 for illustrating the action 

 of the two metals is to 

 take a strip of each, and 

 solder or fix to each strip 



a piece of wire (Fig. 5). These wires can then be made to touch, 



and thus we shall have a complete circuit, the electricity starting 



from the zinc plate, passing through the liquid and the copper, 



and then back by the wire ; at the same time wo shall be able 



to observe tho effects produced on each plate better than we 



could when they were in contact. If we place the ends of the 



wire clot-e together upon the tongue, we shall be able to taste 



the electricity, and thus see that a current is actually passing. 



It is important for us to remember that a faint current can be 



obtained if the plates are merely placed in water, and that 



i the reason why diluted sulphuric acid is used instead, is that it 



is a better conductor, and at the same time it removes rapidly 



I the oxide which forms on the surface of the zinc, and which 



! would seriously retard its action were it allowed to accumulate. 



The real action of the couple is as follows : The zinc having 

 an attrition for czygen decomposes the water, setting free the 



