A. M. Mayer on '■^the electro-tonic stated 21 



3 of A'B' are united by a conductor, the nega- 

 tive electricity of a' unites with the positive of h\ and at the 

 same time the contrary electricities of each of the particles of a', 

 &', c', d\ e', /, g' combine, and thence there results a current 

 which progresses in the conductor from B' to A' and from A' 

 B' in the wire A'B' itself Thus A'B' is traversed, in this case, 

 by a current directed in the same direction as the inducing cur- 

 rent. The state of electric tension which exists in the wire A' 

 B' whilst the current traverses A B is that whicli Faraday has 

 called electro-tonic ; and the cessation of that state produces the 

 second current of induction, while its creation produces the 

 first. * * * * In reality in the above theorj- which we 

 have given, the production of the two instantaneous induced 

 currents is altogether similar to that which passes in the charg- 

 ing and discharging b}^ cascade of several consecutive Leyden 

 jars, in which the inner coating of each communicates with the 

 outer coating of the preceding one." De la Eive then shows 

 how this hypothesis is applicable to the explanation of the pro- 

 duction of induced currents, by the approach and recession of 

 a current in reference to a closed circuit ; to the production of 

 induced currents by magneto-electric currents; and to all the 

 facts embodied in Lenz's laws. 



It appears to me that the truth of the above hypothesis can 

 be tested in the following manner. A closed metallic circuit 

 (which we will call the secondary wire), is in proximity to a 

 wire carrying a voltaic current, (which we will call the primary 

 wire), which produces in the former powerful induced currents, 

 on making and breaking battery contacts. While in these cir- 

 cumstances, we pass through the secondary wire a direct cur- 

 rent, and measure with precision its intensity ; then an exactly 

 equal current is passed in an inverse direction, and its intensity 

 measured. Now, if as De la Eive supposes, the secondary wire 

 be in a state of polarization like in character but inverse in di- 

 rection to that produced in the primary by the passage of the 

 current, there will be a diminution in the intensity of the cur- 

 rent which traverses the secondary wire in a direction opposed 

 to this polarization, while that traversing it in the direction cor- 

 responding to this polarization, will have the same intensity as 

 when it traverses the secondary wire, when the primary current 



< m its proximity. 



Four conditions have to be fulfilled i 



First, a strong inductive action must be brought to bear upo 

 the secondary wire ; 2dly, this action must be produced by 

 constant current ; 3dly, the secondary wire must be a good con- 

 ductor, and therefore cannot have in its circuit a liquid battery, 

 wherewith to propagate the current in this wire ; 4:thly, a means 

 must be devised of "producing at will, in the secondary wire, a 



