328 'Neiv Outlines of Chemical Philosophy. 



3. Two bodies electrified with contrary elements attract each 

 other strongly, although an electric plate be interposed between 

 them. 



4. Two bodies electrified with the same element repel each 

 other, although a thin electric plate be interposed between them. 



j^pplkalion of thtse Prnpnties In the Explanation of the 

 Leydtii Phiiil. 



When a Leyden phial is receiving a charge, a succession of 

 sparks passes between the ball of the prime conductor and the 

 ball upon the top of the phial ; whence it is evident, from what 

 has been previously stated, that when one of the elements (ther- 

 mogen for- instance) is thrown into the phial from the prime 

 conductor, the other element (pliotogcn) is attracted out of the 

 phial by the former element, and bv passing through the air in 

 opposite directions they generate combustion. And as soon as the 

 thermogen on the inside of the phial becomes suthcientlv power- 

 ful to act through the two coatings aiul the glass contained be- 

 tween tliem, it repels the element of its own kind into the earth 

 from the outside of the phial, and attracts the contrary element 

 at the same time out of the earth; and as they pass through 

 each other, they generate a spark at the bottom of the phial. 



When all the pliotogen is drawn out of t!ie phial, and an equal 

 portion of thermogen is thro-.vn in, the phial is fully charged ; 

 for then the outside of the phial is deprived of all its thermogen, 

 and its place supplied with an equal portion of the other cle- 

 ment from the earth. 



This is the theory of Mr. Eeles, which appears to be well 

 founded'. Some objections, however, have lately been advanced 

 against it by Mr. Donovan*, which ought not to be passed 

 over in silence ; for, if these objections cannot be answered by 

 incontrovertible facts, the theory of electricity is still involved in 

 obscurity? 



Objectio7i 1. "If the contrary powers are situate on each 

 surface of the charged phial, and if they strongly attract each 

 other through its siibstance, wliy do they not pass through it," 

 since it has been proved that glass is permeable to each kind of 

 electricity? 



Answer. This objection will vauisli when it is understood 

 that the coating prevents the two elements from passing through 

 the glass and combining. This conclusion nuist be admitted as 

 a just one, since an uncoated phial cannot be charged ; for these 

 elements pass through glass as freely as light. More light will 

 pass through thin gliss than thick, and the same law seems to 

 obtain in electricity. 



* Phil. Mag. vol. xliv. p. 406. 



■• Oljection 



