820 



ELECTRICITY. 



remarked, tliat several other bodies besides amber 

 can, by friction, be made to attract light bodies. 

 The observations of Boyle, Otto von Guericke, New- 

 ton, and a few other philosophers of the same period, 

 contributed somewhat to the extension of our know- 

 ledge of electricity ; but it was during the 18th cen- 

 tury, that the most important discoveries ami ii< nc 

 ralizations of the phenomena before known upon this 

 subject were made. 



Hawksbee made several very important discov- 

 eries, and among other improvements he introduced 

 the glass globe for producing electricity. Stephen 

 Grey about the year 1 729, made a numerous set of ex- 

 pertinents with glass tubes and other apparatus, which 

 led to the important discovery, that some bodies are 

 conductors, and others non-conductors, of the elec- 

 tric fluid ; and along with his friend W. Wheeler, he 

 discovered the method of insulating bodies. M. Du 

 Fay soon afterwards inferred the distinction of vitre- 

 ous and resinous electricity, from having observed the 

 difference of effects arising from exciting a body of 

 a resinous nature, compared with bodies of a glassy 

 nature. To the same philosopher is due the merit 

 of introducing the metallic conductor in the electric 

 machine. Von Kleist and Muschenbroek simultane- 

 ously discovered the jar or Leyden phial, and Dr Frank- 

 lin combined these jars in the form of what is called the 

 electric battery. The latter philosopher, by experi- 

 menting on the Leyden jar, was led to the conclusion, 

 that while the one side of the jar (when charged) posses- 

 sed a greater quantity of electricity than its natural 

 share the other side had lost just as much, and that thus 

 while the one side had electricity in excess, the other 

 had it in defect. The distinction which Du Fay had 

 made betweenvitreous and resinous electricity, regard- 

 ing them as different fluids, was by Dr Franklin 

 accounted for, on the principle that one class of 

 bodies were surcharged, and therefore gave out elec- 

 tricity, others were under-charged, and were disposed 

 to receive it, the first class he called positive, cor- 

 responding to the vitreous class of Du Fay, and the 

 others he termed negative, the same as the resinous 

 of the French philosopher. Dr Franklin was the 

 first who brought down electricity from the clouds, 

 by means of a kite, and he introduced the conducting 

 rod for preserving buildings from the action of 

 lightning. The more recent history of electricity is 

 so intimately connected with galvanism, that it will 

 be best detailed under that article. 



The order we shall adopt in the present article will 

 be the following : 1. A general statement of electri- 

 cal phenomena, independent of all theory. 2. The 

 theories which have been proposed for explaining these 

 phenomena. 3. Electrical machines. 4. Effects of 

 electrical attraction and repulsion. 5. Distribution 

 of electricity. 6. Transference of electricity. 7. Laws 

 of Induction. 8. Motion of electricity. 9. Chemical 

 effects of electricity. 10. Effects of electricity upon 

 living bodies. 11. Electricity developed by changes of 

 temperature and of form, from contact, compression, 

 and other changes in bodies. 12. Electricity of the 

 atmosphere. 



I. A dry glass rod, a piece of amber or sealing 

 wax, when rubbed briskly with a dry woollen cloth, 

 and immediately presented to light bodies, such as 

 fragments of paper, thread, cork, straw, cotton or 

 gold leaf, will first attract and then repel them. The 

 bodies which have thus acquired this attractive and 

 repulsive power are said to be excited. All sub- 

 stances, however, are not capable of becoming 

 excited ; hence the distinction of bodies into classes 

 electrics, or such as become excited by friction, 

 and non-electrics, or those which, when rubbed, do 

 not display electric phenomena. The principal elec- 

 tric substances in nature are the following : viz. 



amber, gum-lac, resin, sulphur, glass, the precious 

 stones, silk, the fur of most quadrupeds, and almost 

 all vegetable substances which have been thoroughly 

 deprived of moisture, as baked wood, and dry paper. 

 If the light bodies which have been repelled from an 

 excited electric be again presented to it, they will, 

 provided they have touched no other body, continue 

 to be driven off. Some substances remain in com act 

 with the electric longer than others ; fibres of cotton 

 adhere some time, while metallic bodies are repelled 

 the instant after contact. Two bodies, which have 

 both been in contact with the same electric, mutually 

 repel each other. If a glass tube of considerable 

 diameter, and two or three feet in length, be em- 

 ployed for the experiment, we notice in a dark 

 room, during the friction, flashes of light, of a bluish 

 tinge, extending over every part of the tube ; and 

 sparks, attended with a sharp snapping sound, are 

 seen to dart out in every direction. If we present to it, 

 after vigorous rubbing, a round metallic ball, sparks 

 will be obtained as the ball approaches the tube ; 

 and if the knuckle be presented instead of the ball, 

 the same effect takes place, accompanied with a 

 pricking sensation. If a metallic ball be suspended 

 in the air by silk, thread, or fibres of worsted or hair, 

 or a rod of glass, and rubbed while in this situation 

 by an electric, it will exhibit the same properties of 

 attraction and repulsion, as if it had been itself an 

 electric. That the ball should thus be cut off' from 

 contact with any substance, except the air and the 

 electric which sustains it, is essential to the success 

 of the experiment. If an excited electric be placed 

 near a rush-pith ball suspended by silk, the ball will 

 in the first place approach the electric, but after con- 

 tact will recede from it. If now, uncovering the 

 electric, we present to the ball which lias thus 

 touched it a second ball, similarly suspended, but 

 which has had no previous communication with any 

 electric, we shall find that these two balls will attract 

 one another, and come into immediate contact. The 

 iame results are repeated between this second ball 

 and a third, which may be presented to it, and so on 

 in succession, with a continued diminution, however, 

 in the rapidity of the movements, indicative of a 

 diminished power, in consequence, as it would seem, 

 of its being distributed among a number of bodies. 

 From these facts we infer that the electric imparts to 

 the balls, suspended as above, properties exactly 

 similar to those which had been excited in itself by 

 riction. By repeated contact with a number of 

 bodies, an excited electric is found to lose its elec- 

 trical powers, in the same degree as these powers 

 lave been acquired by the bodies themselves ; and 

 resh excitation alone can renew them. It is evident, 

 herefore, that electricity is capable of being trans- 

 'erred, in the same sense as caloric, of which we 

 speak, as being communicable, and, like caloric, it 

 s weakened by diffusion among a number of bodies, 

 [fan electrified ball be touched with the finger or by 

 a rod of metal, it will be deprived of the whole of its 

 electricity, which will pass to the fieger or rod touch- 

 ing it ; the ball being left in its original or natural 

 state, and again becoming susceptible of being at- 

 ;racted, either by an excited electric, or by another 

 dy, to which electricity has previously been com- 

 municated. If a rod of glass be applied instead 01 

 the finger or metallic rod as above, the body touched 

 remains unaffected, notwithstanding the contact. We 

 are thus led to conclude that some substances, such 

 as glass, are incapable of conducting- electricity ; 

 while others, such as metals and the human body, 

 readily conduct it. And it is found that all electrics 

 are non-conductors, while on the contrary, conductors 

 are non-electrics. The permanence of electricity in 

 metallic bodies, suspended in the air by siJktu 



