ELECTRICITY. 



110 



Fig. 1. 



mo 



5 



ELECTRICITY. I. 



HOW OKNri:.\Ti:n DIFFERENT THEORIES CONDUCTORS AND 

 >::., 1'lllI-UALL AND OOLD-LEAF ELECTRO- 



irtmont of Natural Philosophy or Physics to which we 

 now to turn our attention is ono of groat practical itnpor- 

 ,00. It is ono, too, in whieh noarly all tho apparatus re. 



> by tho ntti'lent liimself, if ho possess a little mo- 

 skill and perseverance ; and a large number of experi- 

 ments may bo tried at but little cost. Wo can 

 promise our readers, as they accompany us, 

 in tni' tim.s how to perform such experi- 

 ments as will enable them and their friends 

 :id ir.any a pleasant evening, and at tho 

 : :m" ^ivothom a thorough insight into 

 tho principles of tho science. In fact, there 

 are few things which cause 

 a winter evening to pass 

 more pleasantly than a good 

 electrical machine. 



There are few of tho 

 sciences that have such va- 

 ri d and extensive applica- 

 tions in tho arts and manu- 

 factures as this has. By it 

 our thoughts arc flashed 

 with lig'itning speed to dis- 

 tant pla : :s ; our messages 

 are instantaneously trans- 

 mitted, even, if needs be, in our handwriting ; our clocks are 

 ulated with the utmost accuracy ; our lighthouses, streets, 

 d buildings are illuminated ; our plate is silvered or gilt ; 

 fuzes are exploded ; our bells are rung ; and a thousand 

 her things, of great importance to us in daily life, are done, 

 e may truly say, then, it is an important scieuce. 

 Like most other important things, this science Lad a very 

 iple commencement. Several centuries before tho Christian 

 era, it was found by some Greek philosophers that if a piece of 

 amber was rubbed on a piece of cloth or silk it acquired tho 

 property of attracting light substances, such as fragments of 

 paper or feathers. No further advance was made in the sub- 

 ject, nor was much notice taken of it, except that it was attri- 

 buted to a peculiar property supposed to exist in tbe amber. 

 This property was called electricity, from electron, the Greek 

 word for amber. 



Many other substances beside amber are now found to possess 



this same property cf attracting light bodies when rubbed. 



In fact, all bodies may be said to possess it to a greater or less 



extent. Tho simplest mode of trying the experiment is to take 



a piece of sealing-wax, and rubbing it violently on cloth or 



flannel, hold it near some small scraps of paper. It may be 



seen rather better by taking a piece of glass tube half or throo- 



.uarters of an inch in diameter, and rubbing it with a piece of 



,k, and then holding it to the paper. 



We may mention here that for many electrical experiments 

 iieces of glass tubing are very useful. A pound or two of 

 'erent sizes should therefore be obtained. In largo towns 

 scientific instrument-makers usually supply it at a moderate 

 price, or it may be obtained at any glass-works. If wo want to 

 .t it to any length, wo need merely make a slight groove with 

 triangular file at the required place, and it will easily break 

 pretty evenly. The ends may be rounded by holding them in 

 e flame of gas, or better still, of a spirit lamp. 

 The effect produced by rubbing tho glass tube may bo con- 

 "erably increased by smearing on tho silk rubber a little 

 .ectrical amalgam. This is a compound of mercury, tin, and 

 zinc, which has tho property of greatly increasing tho quantity 

 of electricity produced. There are different recipes for tho 

 preparation of this compound, and cither of the following will 

 act well: Tin 1 part, zinc 2, mercury 6; or, tin 1, zinc 1, 

 mercury 2. If a quarter or half an ounce be taken of tho 

 , and proportional quantities of tho other ingredients, it will bo 

 ifficient for general purposes. The tin and zino should bo 

 melted together in an iron ladle, and should then be poured 

 with the mercury into a wooden box well rubbed with chalk, 

 d tho whole shaken till it cools. Care is required lest the | 

 ury should spirt about when mixed with the hot metal. j 



87 N.E. 



Whon cold, the amalgam may bo pounded, and from time 

 t > titn a little should bo mixed up with lard and smeared on 

 tho silk. 



If now we rub a piece of glass tube violently with this, we 

 shall notice the following effect* : Light bodies will as before 

 bo attracted towards it, and as soon as they hare touched it 

 will fly away ; if wo hold the finger clone to the tube, and draw 

 it along, a faint crackling noise will bo heard, and, in the dark, 

 sparks or bluish light will bo seen ; on bringing the tube close 

 to the face, a sensation noarly resembling that of cobwebs will be 

 felt, and at tho HUUIO time a faint smell as of burning sulphur will 

 bo porcoivod. These, then, are tho main effects produced by the 

 electricity, and some of them may be seen in other ways. If we 

 take two rounded fragments of quartz, such as may often be 

 picked up on a beach, and rub them together in the dark, we 

 shall observe a similar light and odour. So, too, on a frosty 

 night, if we take up a black cat which has become warm by 

 lying in front of a fire, and stroke it, we shall see and hear small 

 sparks freely given off from its coat, and at times, if one hand 

 be held near tho neck and the other gently passed along the 

 back, small shocks will bo felt. Somo people observe a jmil^r 

 effect if their hair bo dry and they brush it vigorously. 



Now tho question naturally suggests itself, what is the cause 

 which produces these effects that is, what is electricity ? To 

 this we can give no answer. We may say it is an imponderable 

 fluid, or we may call it a subtle but powerful physical agent ; 

 but these are merely terms invented to hide and conceal our 

 ignorance. All that we really know is, what are the effects it 

 produces, and the means of procuring it. 



Electricity may bo obtained in several different ways ; the 

 most important are friction, chemical action, heat, pressure, 

 magnetism, and some vital operations. The two former are the 

 most common modes of producing it ; there is, however, a dif- 

 ference in tho effects according to tho mode by which it is ob- 

 tained, and hence that produced by friction is known as statical 

 or fnctional electricity, while that produced by chemical action 

 is called dynamical or voltaic electricity. Wo shall deal first 

 with the former of these, or frictional electricity. 



We have seen that electricity is generated when we rub a 

 piece of glass tube or sealing-wax : wo want, however, an easy 

 plan of indicating its presence, and tho simplest is by tho electric 

 pendulum represented in Fig. 1. A piece cf glass tube, ten or 

 twelve inches long, is fixed vertically in a s-nall stand ; to the 

 top of this is fitted a wooden cap with a bent wire ending 

 in a hook or loop inserted in it. A 

 small ball, A, cut out of tho pith of 

 the elder, is fixed to a silk thread, and 

 suspended by this from tho hook. In- 

 stead of tho glass support, a piece of 

 wire may bo used, bent over as in the 

 figure; but it does not answer quite 

 as well. Tho reason why elder pith 

 is chosen is on account of its extreme 

 lightness. It is readily obtainable, 

 and with a sharp knife may cosily 

 bo cut into tho shape of a ball. If 

 now an excited glass tube bo held near 

 it, the ball will immediately be at- 

 tracted and riso towards the tube. 

 As soon, however, as it has touched 

 it, tho electricity is shared between 

 them, and tho ball is now repelled as 

 strongly as it was before attracted. 

 If two balls thus mounted bo each 

 allowed to touch tho tube, it will be 

 found that they, too, repel one ano- 

 ther. 



Now vary tho experiment, by bring- 

 ing an excited rod of sealing-wax near 

 tho balls when thus charged ; and we 



shall find that they will at once bo attracted towards it, though 

 they are repelled by the glass tube. 



In the same way we shall find that two balls, mounted on 

 separate stands, and both excited by contact with the sealing-wax, 

 repel each other ; but if one bo excited by the glass tube and the 

 other by the wax, instead of repelling, they will attract one 

 another. This seems to show that there are two different kinds 

 of electricity, one produced by the friction of glass and the other 



Tig. 2. 



