182 1 .] On Franklin's Theory of Electricity. 1 85' 



to explain, how able, intelligent philosophers should be so spell-, 

 bound by an hypothesis, as, in defiance of the plainest observa- 

 tions of their senses, to assume, that in all these instances, the 

 electric spark was just the same, produced by one and the same 

 cause, a single electric .fluid, passing in every case from the 

 plus, or positive, to the minus, or negative conductor. 



These observations on M. Van Marum's paper would be here 

 concluded, but there is another part of it relating to the apparent 

 repulsion of electrified hght bodies, containing a few arguments 

 so novel and original, that though it is not intended generally to 

 enter in this place upon the subject of electrical repulsion, it is 

 difficult to avoid taking some little notice of them. 



M. Van Marum first assumes, that it is " a sound truth, and 

 well confirmed by experience, that no electric force can arise 

 from the surface of a body, unless this latter be in contact with 

 bodies either solid or fluid which assume a contrary force, or be 

 surrounded by such bodies." 



To be sure it has seemed to be placed among the elements of 

 electrical science, confirmed by every experiment, that when 

 bodies having opposite electricities are brought into contact, the 

 electricities, unless controlled by superior attractions, combine 

 and are neutrahsed. But it is not here intended to controvert 

 the bases of the reasoning, but to notice the method of argument, 

 founded upon those bases. ,- 



M. Van Marum proceeds. '* A body positively electrified and 

 placed in the air is, therefore, conformably to this law surrounded 

 with an atmosphere of contrary electric power ; and a negatively 

 electrified body is, on the other hand, surrounded by a positively 

 electrified atmosphere." " It is evident that every electrified 

 body must necessarily be placed i)i the mid^t of this atmosphere 

 of an opposite electric force, the contrary being impossible." 



Now if these propositions were true, it is quite clear that an 

 electrified sphere would form around itself a spherical electrified 

 atmosphere of which the sphere would be in the centre. If, 

 therefore, two similarly electrified pith balls were suspended in 

 contact, they would form around themselves spherical atmo- 

 spheres having an opposite electric force to themselves, fig. 7. 

 The pith-ball A would be surrounded by the atmosphere CDEF, 

 and the pith-ball B by tie atmosphere C G E H. It is evident 

 that the centre of the joint atmospheres would be at the point of 

 contact of A and B, to which, therefore, they would both be 

 attracted, and consequently would remain at rest. But these 

 atmospheres would not suit M. Van Marum's hypothesis, nor is 

 it consistent with the facts that the pith-balls should remain at 

 rest. These difficulties are most ingeniously overcome, by 

 M. Van Marum's supposing that the pith-balls A and B, fig. 8, 

 should form atmospheres round centres C and D at a distance, 

 and then that each atmosphere would attract its pith-ball to that 

 centre. Why the balls should form atmospheres round those 



