Measure of the relative Tetisiofi of Electric Currents. 267 



are ever attended with any such result; but that when changes 

 have apparently taken place, it is probable that they may be 

 directly traced either to a disturbance at the place of genera- 

 tion, or to the development of other currents of a different 

 character, the primary current itself remaining unchanged. 



3rd. That there are two different methods of accomplishing 

 these disturbances, and thereby of raising the elastic force 

 of a current : 1st, that tension may be augmented by the 

 sacrifice of quantity; Volta's plan of a reduplicated series, and 

 Henry's ribbon coil in its condition of equilibrium, being ex- 

 amples : 2nd, by the introduction of new affinities in the ex- 

 citing cells ; batteries charged with nitrosulphuric acid or sul- 

 phate of copper are examples. 



4th. That the law which regulates the connexion of this 

 diminution of quantity, or condensation, with the increase of 

 tension, is the same as that which regulates the analogous 

 phaenomena of ponderable elastic fluids. 



Incidentally, the examination of certain other points will be 

 entered upon, for example, a brief consideration of Lenz's 

 law of the conducting power of wires ; this it will be shown 

 holds not only in the case of Faradian currents, but in the 

 direct currents from hydro-electric and thermo-electric pairs, 

 as has been advanced by some philosophers tjut denied by 

 others. 



The terms tension, intensity, tensile effect, &c. have had 

 very different significations attached to them. From this cir- 

 cumstance a great deal of confusion has arisen, and it is one 

 of the causes of that diversity of opinion and contrariety of 

 theory which obtain in the elementary parts of the science 

 of electricity. For example. Dr. Faraday appears to use the 

 words tension and intensity as synonyms, expressive, as it 

 were, of elastic force, — chemical authors generally adopting 

 the same signification ; " The remoteness from the unexcited 

 state, a condition expressed by the terms tension or intensity ^ 

 " By tension or intensity is meant, the energy or effort with 

 which the current is impelled." (Turner, Elem. Chem.) 



This confusion of terms leads to a confusion of facts of a 

 much more serious kind. English electricians uniformly 

 state, that the magnetic needle deviating in the neighbourhood 

 of a current, takes no note whatever of the intensity of that 

 current. Continental writers, almostwithout exception, regard 

 the deviation as a function of the intensity, and the statements 

 therefore appear discordant. Whilst the effect is thus dif- 

 ferently described, all agree as to the facts of the case. In 

 what follows, the term tension will be used as expressive of 

 the elastic force of the current, that power by which it is en- 



