46a Obftrvations on the Theory of EleBric AllraElion. 



confpire to modify, either by giving or receiving the elettrlc fluid, the ftate of the in(er- 

 mediate 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 ele£lrified bodies, 

 than the ftate of the intermediate 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 

 electrical ftate is moft different from its own. On the other hand, when bodies are in dif- 

 ferent ftates of ele£tricity, they will mutually counteract the changes, which they might 

 feparately produce in the ftate of the intermediate air ; but each will operate on the exte- 

 rior air without any compenfation, In this cafe the ftate of the intermediate air will con- 

 tinue 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 according to its refpe£live ftate of eleftri- 

 city. The two bodies therefore, moving towards that part of the furrounding medium, 

 whofe electrical ftate is moft different from their own, will at the fame time move towards 

 each other. 



This theory very ingenioufly avoids the difficulty of explaining the cafe of ele£trical re- 

 pulfion, by refolving it into an attradtion towards the furrounding medium. It feems 

 however to be liable to two objedtions. In the firft place, inftead of afTuming unauthorized 

 principles with the preceding theory, it omits the confideration of one whofe exiftence 

 feems to be afcertained by experiments. If a body be in either ftate of ele£tricity, it will 

 induce in an adjacent body the contrary ftate, until it fliall have come within a certain 

 diftance. This property, which has been afcertained by various experiments, indicates a 

 repulfive force fubfifting between the portions of the electric fluid that belong to the adja- 

 cent bodies; and this theory makes no allowance for fuch a repulfion. The fundamental 

 principle of it is merely a diffufion of the eleftric fluid, and is * thus ftated by M. de Luc : 

 " the eleftric matter tends towards all fubftances,' and the more ftrongly in the fame pro- 

 *' portion in which they pofTefs a fmaller quantity." In the fecond place, it does not ap- 

 pear, when carefully confidered, to afford any alTiftance towards the removal of the grand 

 difficulty, the mutual repulfion of bodies negatively electrified. If two bodies negatively 

 electrified be placed at a fmall diftance, they will both, according to M. de Luc's explana- 

 tion, receive the eleCtric fluid from the intermediate air, which will confequently retain a 

 fmaller portion than the furrounding atmofphere. From the law above-mentioned it 

 fliould follow, that the redundant fluid of the exterior air fliould by difl"ufion be commu- 

 nicated both to the bodies and to the intermediate fpace ; but no reafon appears, which 

 would induce u? to fuppofe that the bodies themfelves fhould recede to a greater diftance. 

 M. de Luc does indeed endeavour to prove that fuch a motion fhould take place, but by an 

 experiment whofe folution contradiCts his own theory. He fufpended by a filk thread a 

 large, but light, metallic ball, and prefented it in a ftate of pofitive electricity to a body 



• " La loi fuivante fufEt feule : La matiere eleftrique tend vers toutes les fubftances, d'autant plus 

 " fortement, qu'elles en poffedeiitnioins." Journal de Phyfique, Juin j/^o. 



4 negatively 



