372 WELLS'S NATURAL PHfLOSOPHT. 



or elements, viz., the vitreous and the resinous electrici- 

 ties. Each kind is supposed to repel its own particles, but 

 attract the particles of the other kind. 



When these two fluids pervade a body in equal quantities, they neutralize 

 each other in virtue of their mutual attraction, and remain in repose ; but 

 •when a body contains more of one than of the other, it exhibits vitreous or 

 resinous electricity, as the case may be. 



738. The theory of a single fluid, or the 

 theory of a thcory propoundcd hy Dr. Franklin, supposes 

 Bing e ui ^^^^ existence of a single subtile fluid, without 



weight, equally distributed throughout nature ; every sub- 

 stance being so constituted as to retain a certain quantity, 

 which is necessary to its physical condition. 



When a substance pervaded by this single fluid is in its natural state or 

 condition, it offers no evidence of the presence of electricity; but when its 

 natural condition is disturbed it appears electrified. The difference between 

 the electricity developed by glass and that by resin is explained by this 

 theory, by supposing electrical excitation to arise from the difference in tho 

 relative quantities of this principle existing in the body rubbed and the rub- 

 ber, or in their powers of receiving and retaining electricity. Thus one body 

 becomes overcharged by having abstracted this principle from the other. 



whatareposi- '^^^' Tlic t WO different conditious of elcctric- 

 tive "efeS- i^Jj which wcro called by Du Fay vitreous and 

 *'^^^ resinous electricities, were designated by Dr. 



Franklin as positive and negative, or plus and minus. 

 Thus a body v/hich has an overplus of electricity is called 

 positive, and one that has less than its natural quantity 

 is called negative. 



The theory of a single fluid has, until quite recently, been generally adopted 

 by scientific men, and tho terms positive and negative electricities are uni- 

 versally used in the place of vitreous and resinous. Within the last few 

 yars, however, some discoveries have been made which seem to indicate 

 that the theory of two fluids is the one which approaches nearest to the truth. 



.„^ ^ . x. In addition to these two theories respecting the nature of 



What 18 Pro- ^ '^ 



fessor Fara- electricity, another has been proposed by Professor Faraday, 



eiec'tridty7 °^ °^ England. He considers electricity to be an attribute, or 

 quality of matter, like what we conceive of the attractioc of 

 gravitation.* 



* It is not easy to perfectly explain to a befrfnner the view which has been talcen by 

 Professor Faraday (who is at present the highest recognized authority on this subject) re- 

 fpecting the nature of electricity. The following statement, as given by a late writer 

 (Robert Hunt), may be sufficiently comprehensive and clear : " Every atom of matter is 



