VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 273 



conductor. It naturally follows, that when the metal plate is afterwards removed 

 from the proper plane, its capacity being lessened so as to remain equal to the 

 100th part of what it was before, the intensity of its electricity must become 

 of 50° ; since, agreeably to the supposition, the intensity of the electricity in the 

 phial or conductor was of half a degree. 



A conductor that is electrified while it stands in full and ample contact with 

 another proper conductor, as above specified, and is afterwards separated from it, 

 shows the same phenomena that are exhibited by a conductor, which, after 

 being electrified, is contracted into a smaller bulk, or contrarywise, like Dr. 

 Franklin's experiment of the can and chain. If a small quantity of electricity 

 applied to the metal plate of the condenser enables it to give a strong spark, it 

 may be asked, what would a great quantity of electricity do ? The answer is, 

 that it would do nothing more, because, when the electricity communicated to 

 the metal plate is so strong as to overcome the small resistance of the inferior 

 plane, it will be dissipated. 



After all that has been said in the preceding pages, it may be easily under- 

 stood, that if the metal plate of our condenser can receive a good share of elec- 

 tricity from a Leyden phial, or from an ample conductor, however weakly elec- 

 trified ; it cannot receive any considerable quantity of it from a conductor of a 

 small capacity ; for this conductor cannot give what it has not, except it were 

 continually receiving a stream, however small, of electricity, as is the case with 

 an atmospherical conductor, or with a prime-conductor of an electrical machine, 

 which acts very poorly, but continues in action. In those cases it has been ob- 

 served above, that a considerable time is required before the metal plate has ac- 

 quired a sufficient quantity of electricity. 



As an ample conductor, weakly electrified, imparts a considerable quantity of 

 electricity to the metal plate of our condenser, so that when the said metal plate 

 is afterwards separated from its proper plane, the electricity in it appears much 

 condensed and vigorous ; so when the same metal plate contains a small quantity 

 of electricity, and such as cannot give a spark or affect an electrometer, that 

 electricity may be rendered very conspicuous by communicating it to another 

 small metal plate or condenser. 



Mr. Cavallo was the first who thought of this improvement, which he de- 

 rived by reasoning on my experiments. He actually made a small metal plate 

 not exceeding the size of a shilling : this 2d condenser is certainly of great use 

 in many cases, in which the electricity is so small as not to be at all, or not 

 clearly, observable by my method or a first condenser only, as has been evidently 

 proved by some experiments we made together. Sometimes the usual metal 

 plate of my condenser acquired so small a quantity of electricity, that being 

 afterwards taken up from the inferior plane, and presented to an extremely sen- 



vol xv. N N 



