2(>1 PHILOSOPHICAL TRANSACTIONS. [ANNO 1782. 



condenser of electricity, for the sake of using a word which expresses at once 

 the reason and cause of the phenomena to be treated of in this paper. 



The whole method may be reduced to the following few observations. — 1. An 

 electrophorus must be procured, the resinous coat of which must be very thin, 

 and either not at all electrified, or, if electrified, its electricity be entirely extin- 

 guished. 2. Its usual metal plate must be laid on this resinous and unelectrified 

 plate, in full and flat contact ; but care must be taken that it does in no point 

 touch the lamina of metal on which the resinous stratum is usually fastened. 3. 

 Those plates being so conjointly placed, a conducting communication, viz. a 

 wire, must be brought from the atmospherical conductor to touch the metal 

 plate of the electrophorus, and to touch that only. 4. The apparatus must be 

 left in that situation for a certain time, viz. till the metal plate may have acquired 

 a sufficient quantity of electricity through the conducting communication, 

 which brings it from the atmospherical conductor very slowly. 5. Lastly, the 

 conducting communication must be removed from the contact of the metal 

 plate : the metal plate is then separated from the resinous one, by lifting it up 

 by its insulating handle, after which it is in a state of attracting, of electrifying 

 an electrometer, or, if the electricity be sufficiently strong, of giving sparks, 

 Sec. at the same time the atmospherical conductor itself shows either no elec- 

 tricity at all, or exceeding small signs of it. 



It was mentioned above, that the conducting wire must be left in contact with 

 the metal plate for a certain time, the length of which however is not easily de- 

 termined, since it depends on variable circumstances. When the conductor 

 itself shows no signs of electricity, then it will be necessary to leave the appa- 

 ratus during 8, 10, or more minutes. But if the conductor itself be capable of 

 just attracting a very small thread, then it will be sufficient to leave the apparatus 

 in contact as above-mentioned, for a few seconds only, in order afterwards to 

 obtain from it very conspicuous electrical appearances. 



Of the electrophorus to be used, it must be remarked, first, that its being 

 very thin is of great importance ; it having been observed, that the thinner the 

 resinous stratum is, the greater quantity of electricity can be accumulated into 

 the metal plate laid on it ; which is the case whether the electricity is brought to 

 it from the atmosphere, or from any other electric power. The thickness of 

 -J-5- of an inch, or that of a common coat of varnish, is very proper ; whereas if 

 the resin was an inch thick or more, the experiments would answer very badly. 

 Also, the surface of the resinous stratum, as well as the under surface of the 

 metal plate, must be as plain and as smooth as possible, in order that the two 

 surfaces may coincide more perfectly when laid on each other. 



Lastly, it deserves to be repeatedly and particularly observed, that the resinous 



