496 Mr. Laming on f he primary Forces of Electricity, 



periineiits that when circular plates of different sizes are 

 charged and brought into contact, each retains a quantity of 

 free electricity directly proportionate to its area ; now plates 

 of this figure are always enveloped in compensating atmo- 

 spheres exactly proportionate in volume to their sizes, for 

 their perimeters and their superficies bear a constant relation 

 to each other. 



26. We have hitherto considered the distance of the com- 

 pensator to be given, and have found that its influence varied 

 in the direct ratio of its quantity; and we now have to remark 

 that if its quantity be constant and its distance variable, the 

 quantity of electricity susceptible of being accumulated in a 

 conductor under its influence will vary in the inverse ratio of 

 the distance ; for the quantity of electricity is as the com- 

 pensation, and compensation varies as the square of the di- 

 stance inversely, and as the square of the quantities directly. 



27. Besides distance and quantity there is yet another 

 cause of fluctuation in the efficiency of compensating bodies, 

 and which we find in their natures. There are many reasons 

 for believing that the atoms of all the different sorts of com- 

 mon matter are not combined with equal quantities of electri- 

 city ; indeed, if the minor electrical attraction be acknowledged 

 to be the cause of gravitation, the quantities of electricity 

 around atoms of different sorts will be directly as their re- 

 spective weights ; and all that we know about the electrical 

 attractions leads us to the conclusion, that if there be elec- 

 trical atoms around common nuclei, those at the greatest di- 

 stances will be held with the least forces. 



28. If therefore two compensators whose natures diff*er as 

 we have thus imagined be alike exposed to the same action of 

 free electricity, the major attraction in each of the atoms will 

 be a retarding force to the major attraction acting on it from 

 a distance; and these will be in equilibrium at a certain 

 point of distance from each of the common nuclei. But this 

 point of distance wilt not he the same in the two bodies. 



Now as all the electrical atoms more distant than that point 

 from their respective common atoms will accordingly be set 

 free, the numbers liberated will not be the same, and there- 

 fore the compensating powers of the two bodies will not 

 be equal. This theoretical inference was thus tested by ex- 

 periment : a pane of glass eleven inches by fifteen inches, 

 being coated in the middle with different substances in suc- 

 cession, one of its coatings was uninsulated, and the compen- 

 sating power of the material of which it was formed estimated 

 by the attractive force of a given charge on an uninsulated 

 disc suspended to the arm of a balance in the opposite direc- 



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