20 



LOCALIZED ELECTRIZATION. 



Let us now examine what occurs wlien an electro-maofnetic 

 apparatus is put in action. A bar of soft iron is placed at a short 

 distance from the poles of a magnet, in such a manner that it may 

 alternately" approach and recede from them by a rotatory move- 

 ment. We place the soft iron at first crossways with the magnet, 

 and complete the circuit of metallic thread, rolled either i-ound the 

 soft iron (as in the instruments of Pixii or of Clark) or round 

 the magnet (as in the instruments of Dujardin or of Breton) by 

 placing between its free extremities either a galvanometer or 

 the living muscle of a frog. If now we communicate a movement 

 of rotation to the soft iron, so as to bring it opposite the poles of 



instantaneous current, at the moment 

 when the circuit formed by the inner 

 thread was either interrupted or com- 

 pleted. Hence the expression "the in- 

 duced current," that of the fine thread ; 

 and " the inductive current," that pro- 

 ceeding from the battery. But it was 

 discovered, after a time, that the spirals 

 of the inductive wire acted one upon 

 another, so as to i)roduce also a special 

 induced current at the moment of opening 

 and of closing the circuit. Tliis special 

 current, distinct from that produced by 

 the battery, but produced in the same 

 wire, was called the extra current. It 

 was next ascertained that separate helices 

 superimposed upon the primary sjiiral 

 traversed by the current from the bat- 

 tery, induced currents one on another; 

 occasioning a succession of secondary 

 induced currents. It became necessary 

 to distinguish these by names. M.M. 

 Henry ( Princeton), Becquerel, Abria, De 

 la Rive,* Pouillet, and others, used the 

 terms currents of the second order, of the 

 tltird, fourth, and fifth orders and so on, 

 for the currents induced in the second, 

 third, foTU-th, and fifth helices. And, by 

 a singular contradiction, they retained 

 the term extra current, for the current 

 induced in the first helix; and they 

 called the inductive current, or current of 

 the battery, the current of the first order. 

 They knew, however, that the extra cur- 

 rent, produced, as has been said, by the 

 action of the inductive current upon its 

 own spiral, behaved in all respects like 

 the other induced currents, with which 

 it ought to be classed. 1 have thought it 

 most reasonable to call this extra current, 

 the first current induced, the induced cur- 

 rent of the first order, after the principle of 

 nomenclature established by the physicists 

 above cited. In my electro-dynamic and 

 electro-magnetic instruments, in which 



the two threads occupy the places of the 

 first and second spirals, or superimposed 

 helices, mentioned above, we obtain the 

 induced currents of the first and of the 

 second order. 



I'his brief historical retrospect exhibits 

 the insufficiency or confusion of the no- 

 menclature hitherto emj^loyed. For those 

 not familiar with a certain conventional 

 language (and few practitioners are thus 

 familiar), the names first, second, and 

 third order would indicate cm-rents of the 

 same kind, but classed according to their 

 distinctive characters or theii* superposi- 

 tion, while the name extra current would 

 appear to indicate one of another kind. 



There is yet another source of confusion 

 in the received nomenclature, in which 

 some call the current of the battery the 

 current of the first order, while others call 

 it the inductive current, and reserve the 

 name current of the first order for that of 

 the second spiral. Finally, M. de Moncel 

 distinguishes the currents of the first two 

 helices as the primary ami the secondary 

 currents. Which of all these is the 

 classical nomenclature ? 



In electrodynamic instruments, instead 

 of excluding, so to speak, the current of 

 the first helix from the family of induced 

 currents, it will be found, I think, more 

 reasonable and more philosophic to call 

 it the current of the first order ; since 

 the other currents superior to it have 

 been distinguished by physicists, accord- 

 ing to the superposition of the helices 

 traversed, as the currents of the second, 

 third, fourth, fifth, and sixth orders. But, 

 in order to avoid any confusion with 

 terms already in use, I propose, in place 

 of calling the extra current the current 

 of the first order, to call it the current of 

 the first helix ; and to call the current 

 next superior to it the current of the 

 second helix. 



De la Rive, Trdite d'electricite theorique et appliqiwe. Paris, 1854. 



