342 WRITINGS OF JOSEPH HENRY. [1855- 



If the charge be very large, and the conductor small, it 

 will probably pervade the whole capacity, and as we have 

 seen, in some cases, will convert into an impalpable powder or 

 vapor the solid particles. Because electricity in a state of 

 rest is found distributed at the surface of a body, it was im- 

 mediately assumed without examination, that electricity in 

 motion passes along the surface ; but this conclusion was 

 supposed to be dis-proved by the fact that the conducting 

 power of a wire for galvanic electricity is in proportion to 

 the area of the cross-section, from which it follows that this 

 kind of electricity pervades the whole mass of the conduc- 

 tor. But galvanic electricity differs from common electric- 

 ity, apparently in the exertion of a much less energetic re- 

 pulsion, and in a greater quantity developed in a given time. 

 The deduction therefore from the experiments with galvan- 

 ism can scarcely be considered as conclusive in regard to 

 frictional electricity. 



To settle this point, the writer devised a series of experi- 

 ments which fully proved the tendency of electricity of high 

 tension, (that is of great repulsive energy,) to pass along the 

 surface. It will be sufficient to give as an illustration of 

 this fact, the result obtained by the arrangement represented 

 in Fig, 11, in which C Z) is a copper wire, (one of the best 



conductors of electricity,) of the size usually employed for 

 ringing door-bells, passing through the axis of an iron 

 tube, or a piece of gas-pipe, A B, about three feet long. 

 The middle of this wire was surrounded with silk, and 

 coiled into a magnetizing spiral, into which a large sew- 

 ing-needle was inserted. The wire was supported in the 

 middle of the tube by passing it through a cork (covered 

 with tin-foil), at each end, h i, so as to form a good me- 

 tallic connection between the copper and the iron. Two 



