Royal Society. 437 



cess of accumulation. By increasing or diminishing the distance be- 

 tween the discharging balls, the value of the unit may at pleasure be 

 rendered great or small. 



A series of experiments is described, showing that when a given 

 quantity of electricity is divided among any number of perfectly simi- 

 lar conductors, the attractive force, as measured by the electrometer, 

 is inversely as the square of that number ; and if different quantities 

 of electricity be communicated to the same conductor, their attractive 

 forces are directly as the squares of those quantities. 



The author observes that the electrical force exerted by one body 

 on another is always diminished by the vicinity of a neutral body ; 

 an effect which is analogous to the operation of screens in diminish- 

 ing the force of a revolving magnet on metallic disks, as noticed by 

 him in a former paper, published in the Philosophical Transactions*. 

 It appears, thus, that there is, in all these cases, a portion of elec- 

 tricity, which is masked, and not appreciable by the electrometer. 

 The author proposes to distinguish the terms tension and intensity, as 

 applied to electricity ; expressing by the first, the actual elastic force 

 of a given quantity, accumulated in a given space ; and by the second, 

 the action of that part which is in a state of freedom, and which is in- 

 dicated by its effects on the electrometer. 



Experiments are next related, which were made for the purpose of 

 showing the incorrectness of the explanation of the above fact pro- 

 posed by Mr. Singer, namely, that it depends on the electrical action 

 of the atmosphere. In the transmission of electricity between con- 

 ductors placed at a distance, the quantity required to produce a dis- 

 charge is directly as the distance; and conversely, the distance is di- 

 rectly as the quantity. This distance will, therefore, be a measure of 

 the tension ; whereas the attractive force, as indicated by the elec- 

 trometer, is a measure of intensity only. Another conclusion deduced 

 from this train of reasoning is, that the resistance of the atmosphere 

 to the passage of electricity is not really greater through any one 

 discharging distance than through another, and is in no case greater 

 than the existing atmospheric pressure ; and it was found by direct 

 experiment, that the distance through which a given accumulation of 

 electricity could be discharged, is inversely as the density of the in- 

 terposed air. When this air preserved its density unaltered, the ele- 

 vation of its temperature produced no difference in its power of con- 

 trolling the escape of electricity; hence it is concluded that heated 

 air is no otherwise a conductor of electricity, than in as much as it 

 has thereby become rarefied ; but heat applied to solid conductors 

 was found to diminish their conducting powers. 



The electrical capacities of conducting bodies of different shapes 

 was the subject of inquiry. In plates having the form of parallelo- 

 grams, the relative capacities, when the areas are constant, are in- 

 versely as the sum of the length and breadth ; and when this latter 

 sum is constant, the capacity is inversely as the area. The capacity 



* An abstract of this paper will be found in Phil. Mag. and Annals, N.S., 

 vol. x. p. 21)8. — Edit. 



