1835.] the Advancement of Science. 207 



Magnetism, and Bonnycastle's Mathematical Theory, which 

 agrees with experiment, and with Poisson's theory, applied 

 to magnetism. 



He appeared to consider that theory untenable, which 

 supposes the existence of one fluid only. He brought for- 

 ward examples of the distribution of the electric fluid on 

 the surfaces of solids of different forms, which were readily 

 accounted for, on the theory which assumes the existence of 

 two fluids. In connexion with this subject, allusions were 

 made to some statements and experiments of Mr. Harris, 

 presented to a former meeting of the Association. Mr. W. 

 shewed that similar objections were made to that magnetic 

 theory which required the admission of one fluid only, but 

 that these were not applicable to a theory founded on the 

 supposition of two fluids. 



Mr. Harris explained, and endeavoured to show that 

 there is no law for the diffusion of the electric fluid on 

 surfaces of different forms, or of different sizes. He illus- 

 trated his position by reference to the loaded Leyden jar, 

 which receives exactly the same charge, whether it is in 

 part filled with a metallic body, or is simply coated with a 

 film of metal on its inside. He also pointed out the fact, 

 that the quantity, or size, or shape of the metallic rods 

 outside the jar, has no influence on the charge, which is 

 found concentrated on that part of its surface which is 

 nearest the glass. Mr. H. applied the same principles to 

 explain the nature of the charge on air. Several members 

 expressed their opinions for and against both views. It was 

 admitted that Coulomb's theory of diff'usion is true in a 

 perfectly imaginary case, but that, in practice, it never can 

 be exactly true, on account of the pressure of surrounding 

 bodies, all of which exercise a greater or less influence in 

 concentrating the electric fluid on that portion of the surface 

 which is opposite to each. 



The charge of the intervening plate, it was observed, was 

 independent of the conductors, and the amount of electricity 

 in a body cannot be ascertained but by bringing another body 

 towards it. Hence, the results are uncertain. Mr. Whe- 

 well replied, that the same results were obtained when the 

 connecting body was different ; and, therefore, the experi- 

 ment was not liable to uncertainty. 



