of Etcctricif}/, 107 



..free passage there could be no charge, and on the contrar^', 

 l)oth phiiils arc found charged ; and upon this principle'a 

 battery is easily constructed : hence it becomes necessar}' to 

 assume that electrics contain a large and equal quantity of 

 the electric fluid at all times ; that no real accumulation of 

 quantity can take place ; but that by aflbrding an oppor- 

 tunity to one side for .the escape of this fluid, it is possible 

 to transfer an equal quantity to the other, while the deli- 

 Cicncy is balanced by an occult principle of repulsion. 



It is certainly very difiicult to imagine the existence of a 

 substance capable of yielding a large supply of a peculiar 

 fluid, and into which an additional quantity may be poured 

 on one side while it is abstracted from the other, when, 

 21 the same time, it refuses a passage to this fluid throuo-h 

 its pores : this, how ever, is presumed to be the case in elec- 

 tricity. Dr. Franklin once imagined that, in the process 

 of cooling, the middle of a glass plate or jar might become 

 condensed, and its particles so much concentrated, that, 

 Avhile it admitted a circulation of electric fluid on its sur- 

 face, it refused it through its substance. Dr. Franklin as 

 usual reduced his conjecture to experiment, by grinding a 

 thick glass plate away beyond the middle, and found that it 

 received a charge with as much facility as before, and im- 

 mediately acknowledged the fallacy of this opinion. I 

 should feel exceedingly gratified to aflbrd the society some 

 light upon this curious circumstance; but as my own con- 

 ceptions arc involved in profound obscurity, it would be a 

 vain and fruitless attempt to ofter a fanciful solution un- 

 supported by experiment or by probability. 



The division between the two species of electrics is so 

 fully detailed in the body of the flfth proposition, that it 

 will be unnecessary to support it by any other consideration 

 than an appeal to facts which are generally known. The 

 construction of Mr. Nairne's machine is an ingenious ex- 

 cnipliiication of its truth ; but with respect to'the reason 

 w hich determines these bodies in one instance to receive 

 from, and in other circumstances to yield to, the rubber a 

 supply of electric fluid, we pretend not to assif^n any. We 

 have examined in the first proposition the presumption 

 wliieh these plucnomenaaBbrd of the existence of two fluids, 

 and endeavoured to show that such presumption was ovcr- 

 tiirovvn by the possibility of producing either nctjative or 

 positive electricity by the adaptatiui. of proper rubbers. The 

 following tabic of excitation is extracted from Enajclopcedia 

 llntannka. 



