ELECTRICITY. 



disposing them in the order best fitted 

 for instruction. It is to be lamented 

 that there exists as yet no general and 

 comprehensive treatise embracing the 

 whole of these extensive and compli- 

 cated subjects of modern research ; and 

 that the student has still to gather the 

 information he seeks from a multitude 

 of journals and other miscellaneous 

 sources, where they lie irregularly scat- 

 tered, and are not to be arranged, or 

 even found, without a great expenditure 

 of time and labour. It is the aim of 

 these treatises to supply, in some degree, 

 this deficiency, in as far, at least, as 

 relates to the instruction of those who 

 have no previous acquaintance with the 

 subject, and are desirous of being initi- 

 ated in the principles of the science. 



(3.) In order to convey the clearest 

 and most philosophical views of the sub- 

 ject we are about to treat, we shall begin 

 by stating, independently of all theory, 

 the most general facts relating to Elec- 

 tricity ; presenting them at first in their 

 simplest form. We shall, in the se- 

 cond place, review the theories which 

 have been framed for the purpose of 

 connecting these facts in the mind. We 

 shall thus be enabled, lastly, to study 

 their combinations, to unravel their com- 

 plicated results, and to follow them in 

 their practical applications. 



(4.) The general facts relating to 

 Electricity may be reduced to the six 

 following heads : 



1. EXCITATION. 



2. ATTRACTION. 



3. REPULSION. 



4. DISTRIBUTION. 



5. INDUCTION. 



6. TRANSFERENCE. 



1. Of Excitation, Attraction, and 



Repulsion. 



(5.) If a piece of amber, or sealing- 

 wax, or a smooth surface of glass, per- 

 fectly clean and dry, be briskly rubbed 

 with a dry woollen cloth, and imme- 

 diately afterwards held over small and 

 light bodies, such as pieces of paper, 

 thread, cork, straw, feathers, or frag- 

 ments of gold leaf, strewed upon a table, 

 these bodies will be seen to fly towards 

 the surface that has been rubbed, and 

 adhere to it for a certain time. The 

 surfaces which have acquired by fric- 

 tion this attractive power are said to be 

 excited ; and the substances thus sus- 

 ceptible of excitation are termed elec- 

 trics, in contradistinction to such as 

 are not excitable by a similar process 



and which are, therefore, termed non- 

 electrics. 



(6.) The principal electric substances 

 in nature are the following : viz. amber, 

 gum-lac, resin, sulphur, glass, talc, the 

 precious stones, silk, the fur of most 

 quadrupeds, and almost all vegetable 

 substances (excepting charcoal), which 

 have been thoroughly deprived of mois- 

 ture, as, for example, baked wood, and 

 very dry paper. 



(7.) After the bodies which had been 

 attracted by the excited electric have re- 

 mained in contact with it a certain time, 

 the force which held them together 

 ceases to operate : the bodies then re- 

 cede from the electric, and if the latter 

 be again presented to them, they will, 

 provided they have touched no other 

 body, be repelled, or driven off, instead 

 of attracted. This change from attrac- 

 tion to repulsion takes place more 

 slowly with some substances than with 

 others : some bodies will adhere to the 

 electric a considerable time before they 

 recede ; while others, and especially me- 

 tallic bodies, are repelled the instant 

 after contact : the reason of this will 

 afterwards be seen. 



(8.) It is also to be noticed that two 

 bodies which have both of them been 

 in contact with the same electric, mutu- 

 ally repel each other. 



(9.) The phenomena of electrical at- 

 traction and repulsion are best observed 

 when electrics of considerable size are 

 employed. For the experiments we are 

 about to describe, it is convenient to 

 have them of a cylindrical shape, which 

 admits of their being more easily carried 

 in the hand, and more readily trans- 

 ferred to wherever we may wish to place 

 them. We may employ as our electric 

 a thick cylinder of sealing wax, or one 

 of sulphur. If glass be chosen, it should 

 be in the form of a tube of considerable 

 diameter, and should, previously to the 

 experiment, be gently warmed before 

 the fire, in order to expel all moisture 

 from its surface. As a rubber we may 

 use a silk handkerchief, a piece of clean 

 flannel, or the fur of a quadruped ; but 

 the material which produces the greatest 

 effect when rubbed with glass is an 

 amalgam (or mixture) of mercury with 

 tin or zinc. Whatever be the substance 

 employed, it should be perfectly dry ; 

 to ensure which condition it should, pre- 

 viously to being used, be held for some 

 time before the fire. 



(10.) When, by attending to these pre- 

 cautions, a sufficiently powerful excite- 



