8 ELEMENTARY LESSONS ON [CHAP. i. 



the minus sign ). These terms are, however, purely 

 arbitrary, for in the present state of science we do not 

 know which of these two states really means more and 

 which means less. It is, however, quite certain that 

 electricity is not a material fliiid, whatever else it 

 may be. For while it resembles a fluid in its property 

 of apparently flowing from one point to another, it differs 

 from every known fluid in almost every other respect. 

 It possesses no weight ; it repels itself. It is, moreover, 

 quite impossible to conceive of two fluids whose proper- 

 ties should in every respect be the precise opposites of 

 one another. For these reasons it is clearly misleading 

 to speak of an electric fluid or fluids, however convenient 

 the term may seem to be. Another theory, usually known 

 as the molecular theory of electricity, and first dis- 

 tinctly upheld by Faraday, supposes that electrical states 

 are the result of certain peculiar conditions of the mole- 

 cules of the bodies that have been rubbed, or of the 

 " ether " which is believed to surround the molecules. 

 There is much to be said in favour of this hypothesis, 

 but it has not yet been proven. In these lessons, there- 

 fore, we shall avoid as far as possible all theories, and 

 shall be content to use the term electricity. 



7. Charge. The quantity of electrification of either 

 kind produced by friction or other means upon the surface 

 of a body is spoken of as a charge, and a body when 

 electrified is said to be charged. It is clear that there 

 may be charges of different values as well as of either 

 kiud. When the charge of electricity is removed from 

 a charged body it is said to be discharged. Good 

 conductors of electricity are instantaneously discharged 

 if touched by the hand or by any conductor in contact 

 with the ground, the charge thus finding a means of 

 escaping to earth. A body that is not a good conductor 

 may be readily discharged by passing it rapidly through the 

 flame of a spirit-lamp or a candle ; for the flame instantly 

 carries off the electricity and dissipates it in the air. 



