INFLUENCE OF THE AIR ON ELECTRIFIED BODIES CONSIDERED. 223 



hitherto universally received acceptation of the former, it relates especially to the in- 

 dications of the electrometer, which are found by experiment, all other things being 

 the same, to vary in certain cases with the square of the density ; whereas the latter 

 is expressive of the relation of the whole quantity accumulated to the space occupied, 

 and is always in the direct simple ratio of the density*. 



25. But in these reasonings on the probable source of electrical phenomena, we 

 must not overlook the evidences in favour of electricity being a fluid, operating for 

 the most part by attraction alone, without regard to its elasticity, according to the 

 laws observable in cases of simple pressure, its peculiar property being a tendency to 

 a state of equal action ; hence it endeavours, when accumulated in given points, to 

 flow upon surrounding masses, thereby producing currents, and the various pheno- 

 mena of electrical induction. 



26. It is not essential that I should here enter upon the merits of the above hypo- 

 thesis ; but supposing it to rest on an adequate induction of facts, then it is clear that 

 the term tension would be ill applied, as expressing other than elastic power : we 

 should rather employ some such term as pressure, which would be immediately asso- 

 ciated with altitude or thickness of the electrical stratum. We might, however, still 

 retain the term intensity as expressive of the operation of either the whole or part of 

 the pressure in a given direction, and employ it to measure the quantity on a given 

 surface by the aid of its known relations. 



27. It has been supposed by the late Mr. Singer, in his excellent work on Elec- 

 tricity, that the diminished intensity observable in disposing a given quantity on an 

 extended surface is altogether referable to the attractive force of the atmosphere, to 

 the influence of which the electric particles become more extensively exposed : this 

 view, however, seems inconsistent with experience. 



1°. In disposing half the quantity on a given surface, we find the intensity reduced 

 to one fourth ; now the extent of the atmospheric contact is in this case unchanged. 



2°. The attractive force exerted between electrified bodies and neutral non-con- 

 ducting matter is inconsiderable, so as in some cases to be indefinitely small in respect 

 of the more sensible forces under investigation : hence in experiments similar to those 

 already described (20.), with an opposed semi-conducting or non-conducting plane w, 

 fig. 9, the attractive force was found eventually to be exceedingly small. 



3°. It is apparently at variance with more direct experiments, as in the following 

 instances. 



(/.) A brass ball, b, fig. 11, about two inches diameter, being placed in the centre 

 of a large receiver, and extremely well insulated, was connected with the electroscope, 

 A, by means of a brass rod passing airtight through a collar fixed in a glass plate 

 and socket, ; a quantity of electricity was then communicated to the ball sufficient 



* Should we employ the term intensity to designate any phenomenon of tension, it can only be to express 

 its force in a given direction ; we should therefore understand clearly what is expressed by the compound term 

 intensity of the tension, as measured by the electrometer. 



2 g2 



