SINGLE-FLUID THEORY. 141 



others had prepared the way. The single-fluid 

 theory is described in Priestley's " History of 

 Electricity " as follows : 



" When the equilibrium of the electric fluid, dispersed 

 through the pores of all bodies, is not disturbed, and 

 when there is in any body neither more nor less than its 

 natural share, it does not discover itself to our senses by 

 any effect. The action of the rubber upon a body dis- 

 turbs this equilibrium by producing a deficiency of the 

 fluid in one place, and a redundancy in another place ; 

 and a mutual attraction of the particles of the fluid is 

 excited to restore the equilibrium. If two bodies be both 

 overcharged, the electric atmospheres repel each other, 

 and both bodies recede from one another to where the 

 fluid is less dense ; the electric atmosphere carrying the 

 bodies along with it." 



But, unfortunately for this theory, bodies sup- 

 posed to be devoid of the electric ether, or in a 

 negative state, are found to repel one another 

 precisely like those containing an excess, or in a 

 positive state. This fact discredits the single- 

 fluid theory. 



If the electric ether be a material medium, it 

 must be subjected like all other matter to the same 

 mechanical law of "equal action and reaction in 

 opposite directions." The ether occupying the 

 surface of the rubber, when put in motion trans- 

 fers the impulse it receives to the similar electric 

 ether occupying the rubbed body ; and, being an 

 elastic fluid, recoils by impact, and verifies the 

 general mechanical law of the development of two 



