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divergence of the balls of an eledrometer, included in the receiver 

 of an air-pump, is continually diminiflied during the progrefs of 

 exhauftion ; he confiders it as proved, that the caufe of all elec- 

 trical movements, whether of attradion or of repulfion, is the 

 adlion of the air. This principle he applies in the following 

 manner. When two bodies are in fimilar ftates of eledricity, ei- 

 ther pofitive or negative, they will confpire to modify, either by 

 giving or receiving the eledric fluid, the ftate of the intermediate 

 air, whilft that of the exterior air is only modified by either of 

 them fingly ; and therefore the ftate of the exterior air will differ 

 more from that of the eledrified bodies, than the ftate of the in- 

 termediate air. In this cafe he contends that a repulfion muft 

 take place, becaufe each body muft move towards that part of the 

 furrounding medium, whofe eledrical ftate is moft different from 

 its own. On the other hand, when bodies are in different ftates 

 of eledricity, they will mutually counterad the changes, which 

 they might feparately produce in the ftate of the intermediate air ; 

 but each will operate on the exterior air without any compenfation. 

 In this cafe the ftate of the intermediate air will continue to- differ 

 from that of each body as much as at the firft inftant, whilft the 

 ftate of the exterior air is feparately modified by each body accord- 

 ing to its refpedive ftate of eledricity. The two bodies therefore, 

 moving towards that part of the furrounding medium, whofe elec- 

 trical ftate is moft different from their own, will at the fame time 

 move towards each other. 



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