132 ANNUAL OF SCIENTIFIC DISCOVERY. 



duccd current; that which is nearest to the conducting rare being called the 

 'induced current of the first order,' and the next of ' the second order,' and so on. 



" The currents employed by 31. Duchenne, and about the different proper- 

 tics of which so much has been said and written, are the 'extra current' in 

 the conducting wire, and an 'induced current of the first order' in a parallel 

 wire ; and M. ISecquerel states, that for Duchenne to designate them induced 



currents of the first and second order respectively : ' c'est creer un 



Ian gage tout a fait different de celui qui est employe par tous les physicians ' 

 (p. 89). 



" The most striking differences between these various currents are to be 

 referred to their degree of intensit} T , and this is determined by different con- 

 ditions, of which the following are the most important. The ' initial current ' 

 is intense in proportion to the number of the active cells in the battery, the 

 nature of the electrolytes employed, and the integrity of conducting mate- 

 rials throughout the whole circuit. The force of the ' extra-current' is deter- 

 mined by the same circumstances; but that of the ' induced currents ' depends 

 partly upon these, and also upon other conditions viz., the size of the wire, 

 the length of it which is brought into proximity Avith the conducting wire, 

 and the presence and degree of additional magneto-electric induction. 

 Ccctcris 2xtribus, the finer the wire and the greater its length, the more intense 

 is the induction. 



" In order to obtain great, and at the same time convenient, length of the 

 wires, they are twisted into the form of a hollow spiral, or helix, the latter 

 becoming, in itself, endowed with magnetic properties, one end of the helix 

 being a north and the other a south pole. If into the hollow of this spiral or 

 helix, there are introduced bars of soft iron or steel, these bars become mag- 

 netic by induction; and thus the electrical force, developed in the battery 

 cells by chemical action, becomes resolved into the con-elated force of mag- 

 netism. But precisely the reverse order of induction may take place in 

 another apparatus, and the 'lifter' of a permanent magnet, around which a 

 copper wire is twisted spirally, at the instant that it becomes a magnet by 

 induction, from contact with the poles of the permanent magnet, develops 

 chemico-polarity, or electricity in the copper wire. The former arrangement 

 is termed ' electro-magnetic; ' the latter, ' magneto-electric.' In the one, elec- 

 tricity is developed from chemical decomposition; in the other, from magnet- 

 ism: but in the former inasmuch as magnetism is induced by the initial 

 current there is, in addition to the 'primary induced current/ that order 

 of induction which exists alone in the latter, and the addition of this is one 

 mode of augmenting the intensity of the current. 



" Thus, then, the initial current develops magnetism in the bars of soft iron 

 which are inserted into the hollow of its helix, and the presence of magnet- 

 ism in these bars, at the moment of its induction, develops an electrical cur- 

 rent in the copper wires ; the intensity of the latter induced current being, 

 cateris paribus, in proportion to the size of the temporary magnet, and deter- 

 mined or regulated by the length to which these soft bars are inserted in the 

 helix. The tension, therefore, of the induced current depends upon that of 

 the initial current, upon the size of the wire, upon its length i. e., upon the 

 number of turns in the spiral and upon the force of magnetism temporarily 

 developed in the bars of soft iron. 



" Whatever form or current is employed, the nature and degree of its 

 physiologic effects /. c., of its power to occasion vital phenomena, as dis- 

 tinct from chemical and thermal are determined mainly by differences in 



