'2()8 PHILOSOPHICAL TRANSACTIONS. [ANNO 1782. 



spicuous signs of electricity ; which shows that the Leyden phial is not quite de- 

 prived of electricity. But if the phial was left so far charged as just to attract a 

 light thread, then if the metal plate were to be touched by the knob of it, even 

 for a moment, it would afterwards, when lifted up, give a strong spark ; and if 

 then it were to be touched again by the knob of the phial, it would afford a 2d 

 spark, hardly smaller than the former ; and thus spark after spark may be ob- 

 tained for a long time, which is a very surprizing experiment. 2dly. Suppose 

 you have an electrical machine in such bad order that its conductor will not 

 afford any spark, but will just attract a thread; then if you let this conductor 

 touch the metal plate of the condenser, and after suffering it to continue in that 

 situation for a few minutes, while the machine is kept in motion, lift up the 

 metal plate, you will obtain from it a strong spark. 3dly. In case the electrical 

 machine acts very well, but its conductor is so badly insulated, that it will not 

 give any sparks, as when the conductor touches the walls of the room, or when 

 a chain falls from it on the table ; then if you let the said conductor in that state 

 touch the metal plate of the condenser, while the electrical machine is in action, 

 the plate will afterwards give sufficiently strong signs of electricity ; which shows 

 the great power this apparatus has of drawing and condensing the electricity. 

 In short, by either of those methods you will obtain some electricity from such 

 bodies as could hardly be expected to give any, even when they are not very dry. 

 Indeed, coals and metals excepted, every other body will give some electricity. 



It is now necessary to give an explanation of those phenomena, the theory 

 of which will greatly facilitate the practical performance of this kind of experi- 

 ments. The whole matter then may be reduced to this, viz. that the metal 

 plate has a much greater capacity for holding electricity in one case, viz. when it 

 lies on a proper plane, than when it stands quite insulated ; as when it is sus- 

 pended in the air by its silk strings or insulating handle, or when it stands on an 

 insulating stand, as a thick stratum of resin or the like. It is easy to compre- 

 hend, that wherever the capacity of holding electricity is greater, there the 

 intensity of electricity is proportionably less, viz. a greater quantity of electricity 

 is in that case required, in order to raise its intensity to a given degree ; so-that 

 the capacity is inversely as the intensity, or the endeavour by which the electricity 

 of an electrified body tends to escape from all the parts of it, to which tendency 

 or endeavour the electrical phenomena of attraction, repulsion, and especially 

 the degree of elevation of an electrometer, correspond. 



That the intensity of electricity must be inversely proportional to the capacity 

 of the body electrified, will be clearly exemplified by the following experiment. 

 Take 2 metal rods of equal diameter, but one of them a foot, and the other 5 

 feet long; and let the first be electrified so high as that the index of an electro- 

 meter annexed to it may be elevated to 60°; then let this electrified rod touch 



