ELECTKi 





ELECTRIOITV. TV. 



u.l.l'ttlNATlNO CrrKOTS : I KL> CONDOCTO 



LKYDKN JAK. 



HA VINO now soon the way in which electricity can be obtained 

 in largo quantities, we have to observe what effect* can be pro- 

 duct < I by it. If we place a brass ball in one end of the con- 

 ductor, and holil tlu> knuckle or another ball near to it, parks 

 will pass, which, if the machine bo working wall, will be soon 

 to bo forked and twisted about somewhat after the manner of a 

 flash of lightning. The reason of this is supposed to be that 

 the particles of dust floating in the air serve aa conductors, and 

 thus regulate tho direction of tho spark. 



If we provide a series of conducting bodies planed a little 

 distance apart, and allow tho spark to pass along them, it will 

 always choose tho shortest path, and will bo broken op into a 

 number of short sparks between each conductor. A groat 

 number of brilliant and instructive experiments may be tried 

 to illustrate this principle. Let a number of rather largo shot 

 be cut nearly through with 

 a sharp knife, or procure a 

 number of split shot, such 

 as are prepared for use with 

 fishing tackle, and fix them 

 on a piece of sewing silk at 

 distances of about one- 

 eighth of on inch apart. 

 Now hold a piece of this 

 shot chain to the prime con- 

 ductor, and tho spark will 

 be broken up into a number 

 of short ones between each 

 shot. If, however, wo mea- 

 sure the sum of these inter- 

 vals, we shall see that it 

 is just about tho distance 

 over which the spark would 

 pass if uninterrupted. When 

 tho machine is working 

 well, seven or eight inches 

 of this chain should be illu- 

 minated. 



This experiment may be 

 varied by threading on silk 

 alternate beads of glass and 

 metal, and a string of this 

 kind becomes very prettily 

 illuminated; or metal span- 

 gles or buttons may bo sewn 

 on to a piece of silk ribbon 

 and treated in a similar 

 way. In all these experi- ""^^^^^ 

 menta silk must be used on 

 account of its being a non- 

 conductor. The spark only appears in the interval between tho 

 conductors, and hence, if cotton were employed, the electricity 

 would pass quietly along without producing any luminous 

 effect. 



Another very pretty experiment may be tried in a similar 

 way. Punch a number of small spangles of tinfoil. This may 

 bo done with a punch about one-eighth of an inch in diameter. 

 As, however, the different layers of tinfoil aro very apt to stick 

 firmly together under the pressure caused by the blow, it is 

 better to lay a sheet of paper between each thickness of tho 

 foil while cutting it. Now paste these spangles on a sheet of 

 common window-glass, so as nearly to touch one another, and 

 so arrange them as to form a devico : as, for instance, a star or 

 a cross. Bring strips of tho tinfoil from each end to opposite 

 sides of the glass. When it is dry, and the superfluous pas to 

 wiped off carefully, one of these strips may be held between 

 tho finger and thumb, and the other presented to the conductor; 

 every interval will then be lighted up by the spark, and in a 

 darkened room a very pretty effect will be produced. In mak- 

 ing these devices, care will have to bo taken in arranging tho 

 shape so that the nearest way for tho spark shall be along tho 

 ppangles, for >f by darting across it has to traverse a shorter 

 distance than tho intervals between tno spangles added together, 

 it will be certain to do so. To guard against this, a part of 



96 N.K. 



the spangles hare often to be placed on one side of the g!as 



and tho rest on the other, a .trip of tinfoil passing orar tht 

 edge to connect them. It is a good plan in making the* 

 devices to put them is a frame nude of well-baked wood, and 

 Tarnished with sealing-wax or shellac varniah. This U not, 

 however, absolutely noooMary, a* a split bullet Bay be placed 

 on one ride to take the park by, and the glass held carefully 

 by tho edge, a finger being placed against the other atrip of foil. 

 If it be desired to make a device containing a word, it is 

 better to dispense with the spangles, and paste parallel tripe of 

 tinfoil from end to end of the glass, at a distance of about 

 three-quarters of an inch apart, and then paete a vertical etrip 

 at each end no an to connect the other*. Theme strip* should 

 bo about one-eighth of an inch wide, and should be very care- 

 fully rubbed down, as otherwise the/ are liable to come off 

 afterwards. Now cut away the strips between the alternate 

 bars, first at one end and then at the other, so that the elec- 

 tricity may pass from end to end by the top strip, back again 

 by the next, and so on, thus traversing the whole length. Trace 



your word or device on paper, 

 and, laying the glass over 

 it wherever a line crosses' 

 one of the strip*, make with 

 a sharp knife two crow-cuts, 

 like an X aid carefully pick 

 out the small triangular 

 pieces. Yon will thus have 

 a narrow interval left, at 

 which the spark will appear, 

 and when the whole is com- 

 pleted, and the spark taken 

 with a split bullet fixed on 

 the upper edge, the device 

 becomes clearly lit up. The 

 illustration (Fig. 9) shows 

 the way in which the sheet 

 of glass may be mounted for 

 the lecture-table if so de- 

 sired. 



If a number of the span* 

 gles be arranged spirally 

 round a gloss tube (Fig. 10), 

 and a piece of wood, rounded 

 carefully and covered with 

 tinfoil, be placed at one end, 

 sparks may be token with 

 it, and it will have a very 

 pretty effect Frequently 

 the tube thus prepared is 

 put inside another made of 

 coloured gloss, and in many 

 ways tho effect may, with a 

 little ingenuity, be diversi- 

 fied. The principle of the ,>o 



experiments is an important one, as it explains the effects pro- 

 duced when lightning strikes a house or large building. If we 

 examine any place thus struck, it will be seen that the eloctria 

 iluiil has leaped from one metal fastening or bar to another, 

 displacing the stones or brickwork which lay in its path, and 

 that its course was determined mainly by the position of these 

 conductors. 



If wo take a number of balls of different substances) mounted 

 on wires, and, placing them successively in the conductor, draw 

 sparks from them, we shall find that the colour varies with 

 the substance used. From a brass ball it is almost white; 

 if, however, wo employ a ball of ivory, it will have a crimson 

 tint; and when it ia taken from a gilt surface, it has a 

 greenish hue. The colour is also affected by the medium 

 through which it passes : if tho air be much rarefied it assumes 

 a rc<lder tint, whilo different gases impart different colours to it. 

 Now insert a pointed wire into the conductor, having dar- 

 kened tho room, and notice the effect produced. 



A brush of light will be seen proceeding from the point, 

 and no pparks can be taken from the conductor, for all the 

 electricity ia dissipated. In tho same way, if a pointed wire 

 be held near tho conductor, the electricity will be silently 

 drawn off. Instead, however, of a brush appearing at the end 

 of tho wire, a luminous star will bo seen, tho point 



