46 Mr. Laming on the primary Forces of Electricity. 



move in two directions, and consequently remain stationary ; 

 now if B be divided into two parts in a plane at right angles 

 to a right line passing through the axis of A A', the two parts 

 will instantly separate. 



37. Just so it is in experiment; two balls, for instance, 

 charged with free electricity and in contact, are virtually 

 one conductor; compensated, when freely insulated in the 

 atmosphere, solely by the air. While the two balls are in 

 contact the compensating atmosphere of neither can be per- 

 fect spheres ; and hence it must extend to a greater distance 

 from the surface than if it wholly surrounded each of the 

 bodies individually; and as by Coulomb's law the force of 

 attraction is much greater as the distance is less, the distant 

 particles of compensating air will be brought near to the at- 

 tracting surfaces, and thus by intervening between the balls 

 separate them from each other. 



38. Coulomb has ascertained by experiment that the force 

 with which two bodies equally charged,^ thus apparently repel 

 one another, varies as the square of the distance inversely; 

 which is quite in accordance with the principles we are ex- 

 amining ; for before two bodies can come together the inter- 

 vening air must be removed, and this we have shown to be 

 held against each body with a force varying as the square of 

 the distance inversely ; hence the apparent repulsion of two 

 such bodies will be equal to the sura of the individual forces 

 in each body, but this addition leaves the ratio unaffected. 



39. In the preceding case the charges of the two balls be- 

 ing equal their compensating atmospheres were of the same 

 extent; but we may so dispose the free electricity on two balls 

 that their charges shall be unequal, and then the radii of their 

 compensating atmospheres will differ also. Under such cir- 

 cumstances of course the law of Coulomb will not express the 

 apparent repulsion at all the distances ; this theoretical conclu- 

 sion Mr. Harris has arrived at by the induction of a series of 

 nice experiments made with his very ingenious bifile balance*. 



40. But the influence of the major attraction in causing 

 the divergenceof an electroscope has always to encounter a 

 retarding force in the reaction of the instrument ; and however 

 minute this latter force may be, it must occasion the two com- 

 pensating atmospheres in some measure to intersect one an- 

 other ; with this in recollection we shall easily perceive that 

 one of two charged balls may have so much of its free elec- 

 tricity abstracted as to enter zVs^^ within the compensating 

 atmosphere of its associate, in which event of course instead 



* Phil. Trans. 1836. p. 430 et seq. 



