Scr. XXVIII. ELECTRICAL INTENSITY. 277 



into an indefinite right line. The decrease of intensity 

 seems to arise from some peculiar arrangement of the 

 electricity depending on the extension of the surface, 

 and has been considered by Volta to consist in the re- 

 moval of the electrical particles farther without the 

 sphere of each other's influence. It i's quite independ- 

 ent of the extent of the edge, the area being the same ; 

 for Mr. Snow Hams found that the electrical intensity 

 of a charged sphere is the same with that of a plane 

 circular area of the same superficial extent, and that of 

 a charged cylinder the same as if it were cut open and 

 expanded into a plane surface. 



The same able electrician has shown that the attract- 

 ive force between an electrified and a neutral uninsulated 

 body is the same, whatever be the forms of their unop- 

 posed parts. Thus two hemispheres attract each other 

 with precisely the same force as if they were spheres ; 

 and as the force is as the number of attracting points in 

 operation directly, and as the squares of the respective 

 distances inversely, it follows that the attraction between 

 a mere ring and a circular area is no greater than that 

 between two similar rings, and the force between a 

 sphere and an opposed spherical segment of the same 

 curvature is no greater than that of two similar segments, 

 each equal to the given segment. 



Electricity may be accumulated to a great extent in 

 insulated bodies : and so long as it is quiescent, it occa- 

 sions no sensible change in their properties, though it is 

 spread over their surfaces in indefinitely thin layers. 

 When restrained by the non-conducting power of the 

 atmosphere, the tension or pressure exerted by the elec- 

 tric fluid against the air which opposes its escape, is in 

 the ratio compounded of the repulsive force of its own 

 particles at the surface of the stratum of the fluid, and 

 of the thickness of that stratum. But as one of these 

 elements is always proportional to the other, the total 

 pressure on eveiy point must be proportional to the 

 squares of the thickness. 'If this pressure be less than 

 the coercive force of the ah*, the electricity is retained ; 

 but the instant it exceeds that force in any one point, 

 the electricity escapes, which it will do when the air is 

 attenuated, or becomes saturated with moisture. ' Tt ap- 

 A A 



