174 On the Electric Fluid. 



tlvehj elecfrified" ' Tliis is, it is believed, the theory tiovr 

 generally adopted by electricians, and is probably true as far 

 as it £ocs : but the writer nt" this paper is ot" opinion that the. 

 electrical eft'ccts do not only depend on an adJido/ud quaji- 

 tity in one case, and a loss of the fluid in the other, but on 

 the state of (-o/tdensafion (including in this term compression) 

 and rarefaction (including dilataiion) of the fluid, ihc con- 

 densed state being what is usually called the positive or pluSy 

 and the rarefied the negative or minus state. If the electric 

 fluid be, as is commonly thought, elastic, there is little 

 doubt but that, when an additional quantity is thrown on 

 to a body, it suffers compression ; and, on the contrary, 

 when a portion is taken away, that the remaining fluid is 

 dilated. With non-elastic substances a state of co//(/e«5a- 

 tion, or rather density, may exist without compression ; andy 

 on the contraiy, rarefaction without dilataiion, if the parti- 

 cles of such matter are of different sizes ; for suppose a box 

 were filled with wooden balls of an inch diameter, there 

 w'ould be many vacancies between, which might be filled 

 Up with smaller balls, and the bulk not increased : here 

 would be density without compression: take the small balls 

 away, and there will be rarefuctioii without dilatation. This 

 case w-e can hardly suppose to exist amongst elastic sub- 

 stances, though certainly possible, if each of the particles 

 were at their greatest state of compression or dilatation, and 

 were of dlftereut magnitudes. 



In the Philosophical Magazine, vol. xii. p. 186, an optical 

 experiment was suggested which might perhaps give some 

 iiv.'ight into the two electric states : hitherto there do not 

 seem any decisive experiments which determine the state or 

 the course of the electric fluid. In order to illustrate the 

 hvpothesis here advanced, let the conductor which is con- 

 nected to the cushion, commonly called the negative con- 

 ductor, and the other, or positive conductor, be compared' 

 to the receiver of a common (rarcf^-ing) air puntp and the 

 receiver of a condensing machine (or condensing air pump, 

 as it might be called), both united, as they sometimes are, 

 on one frame • here, whilst the air in one receiver is rare- 

 fied, in the other it becomes condensed. It is, according 

 to the opinion now brought forward, the equilibriuni of 

 toiidensution and compression, not simply of quantity, which 

 produces the shock, the spark, and other electrical effects. 



Would not the terms supplying conductor and receiving 

 conductor be preferable to positive and negative conductor/ 

 Perhaps electrical supplyer and receiver alone would be sufii- 

 eieiTit when speaking of the machine. 



XXX. Pro- 



