Account of an EkBrometeri jj 



point Indicates it at the fame time that it meafures the electric atmofphere ; for inftead of ; 

 a luminous point, a ftar will be obferved upon the ball of the jar, and another at the end 

 of the point. 



Let us now apply this ele£l:rometer to ufeful obfervatlons : 



In order to conne£t the idea of a determinate quantity of fluid to each degree of thf 

 eleftrometer, it is neceflary to compare thefe degrees with the known. quantities. Suppofe 

 for in (lance I have ajar, the coating of which is fix inches fquare ; I ele£irify it til] a 

 fpontaneous difcharge takes place, and remark, by means of Henley's ele£lrometcr, at 

 what degree this difcharge is efFefted. I again eleftrify the jar, till it is nearly faturated, 

 and meafuring with my eleftrometer, I obferve, that the luminous point appears for in- 

 ftance, at two degrees; I then fay, that when my ele£lrometer, applied to an eleftrified 

 body, marks two degrees, the body contains fix inches fquare of eleftricity, I repeat 

 this experiment with a plate of glafs, the coating of which is feven, eight, ten, or twelve 

 ^ fquare inches, and I form a fcale of proportion, which is of tke greateft utility in accurate 

 experiments. , 



In e.ndeavouring to afcertain feme of thefe propofitions, I made an obfcrvation which 

 has convinced me of the utility of my eleftrometer in difcovering the capacity of ele£lric 

 apparatus. Having taken a jar from an eledlric battery, I eledlrified it, and meafured it 

 with a^ point which I pafTed along a ftring of filk ; on obferving the diftance at which the;, 

 luminous point appeared, I joined this jar to another of the fame fize, and imagined that 

 by doubling the quantity of matter, the meafure I had taken would alfo be doubled} 

 on the contrary, however, the latter meafure was not more than about one third of the 

 former : I then added a third bottle, and ftill obtained nearly the fame refult ; whence the 

 following propofition appears to be eftablifhed ; namely, that the extent of the eledric 

 atmofphere is in an inverfe ratio to the quantity of fluid accumulated. Another obfcrva- 

 tion which I have feveral times made, on meafuring the ele£tric atmofphere of a conduc- 

 tor, is, that the limits of this atmofphere form an elliptic figure around the body, nearly 

 fimilar to that reprefented at Fig. 2. 



This, doubtlefs, arifes from the ele£l:rificd body fufpended in a chamber, being nearer 

 to the earth than the cieling ; but it would be a curious experiment to meafure it at an 

 equal diftance from every attra£ling body, in order to obferve whether the fluid has not 

 really a tendency to defcend towards the earth, rather than in any other direiftion. It is 

 my intention to repeat this experiment, as I confidcr it of great importance to afcertain 

 whether eleftricity gravitates towards the globe. 



From thefe firft attempts, I conceive my ek£lrometer would be well adapted for mea- 

 furing the abfolute capacity of Leyden jars,- stnd alfo their capacity with regard to their 

 fize, or to the quality of the glafs of which they are conftru£ted *, for th? latter, by its 

 greater or lefs denfity, abforbs a greater or kfs quantity of fluid* 



Vol. v.— April i8oi. F Inquiries 



