I 



Mr. Laming on the primmy Forces of Electricity, 495 



placed in communication with one that is positively charged, 

 will acquire quantities of free electricity proportionate to the 

 perfection of their compensation respectively ; and the same 

 thing is also true of all the several parts of any charged con- 

 ductor of irregular figure. 



21. Whenever charged bodies are freely insulated in the 

 atmosphere, the air by which they are immediately surrounded 

 is the nearest body, and therefore their compensator; hence 

 the quantity of electricity that may be accumulated in such a 

 conductor under any given intensity will vary in the simple 

 ratio of the quantity of air within a given distance of its sur- 

 face (18.). 



22. Now, in the first place the quantity of air within a 

 given distance of an electrified surface varies directly as its 

 density ; and that the proportionate quantity of electricity 

 susceptible of accumulation in a conductor varies directly as 

 the density of the air, has been completely proved by experi- 

 ment*. Hence the reason of the very minute quantities of 

 electricity only that can be accumulated on conductors placed 

 in what we are accustomed to speak of as a vacuum. 



23. In the second place, the density of the atmosphere be- 

 ing given, the quantity of air within a given distance of the 

 surface of a conductor of irregular figure will be greater as 

 its several parts are more angular or projecting; for example, 

 the cubic contents of the immediate aerial envelops of points 

 are greater than in the case of equal surfaces of any other 

 figure; the cubic contents around convex surfiices are greater 

 than those which are opposite to planes ; and the latter again 

 than when the surfaces are concave ; the aerial envelops of 

 plates of equal area are more voluminous as their perimeters 

 are proportionately more extended ; and the volumes of air in- 

 closing spheres are proportionately greater as the spheres are 

 less. Now the accordance of these several deductions with 

 facts will be recognised on comparing them with the well- 

 known experiments on this subject by Coulomb and Harris. 



24-. The latter philosopher has proved that a charged 

 parallelogram will equally divide its plus electricity with either 

 a cylinder or a prism into which the parallelogram may be 

 supposed to have been formed f; a result which, making very 

 trifling allowances for unavoidable inaccuracies, is quite in ac- 

 cordance with the principles we are considering, for the cubic 

 contents of the compensating atmosphere of those different 

 figures would not be very different. 



25. Mr. Harris has also shown in the same series of ex- 



* Phil. Trans. 1834, p. 228, par. 44 and 45. 

 t Phil. Trans. 1834, p. 233. 



