THE SMITHSONIAN INSTITUTION. 397 



ume of my treatise, (Lehrbuch tier Physik.) If the current of a battery 

 be passed tlirough a voltameter, and then, directly after breaking? the 

 circuit, each of the voltameter phites be brought into contact with the 

 terminating wire of a multiplier, the latter will indicate a current 

 traversing the voltameter in the direction opposite to that of the 

 original current of the battery. This experiment, made as early as 

 1827, by De la Rive, merely shows that an electro-motive opposing 

 force is generated in the voltameter by the primary current ; but it 

 gives us no clue to the cause. 



Becquerel maintained tliat the secondary current appeared only in 

 the case when the poles were immersed in the solution of a salt. 

 Under these circumstances, says Becquerel, the salt is decomposed, 

 the base collects at the negative pole, the acid at the positive ; and if 

 the wires be put in conducting connexion after the removal of the 

 battery, a current is generated in consequence of the re-combination 

 of the acid and base. 



Schonbein now shows that a solution of a salt is not at all necessary 

 for bringing about a secondary current; that the experiment succeeds 

 perfectly with pure water very slightly acidified with pure sulphuric 

 acid, even if the platinum electrodes communicates but for an instant 

 with the battery. 



These secondary currents are by no means of only momentary dura- 

 tion ; they last, according to circumstances, a longer or shorter time. 

 In an instance in which the original deflection of the galvanometer 

 needle by the secondary current amounted to 80°, four minutes elapsed 

 before it altogether disappeared ; in another, when the deflection was 

 1G0°, it lasted thirty minutes. 



Schonbein produced secondary currents as well with electrodes of 

 gold as with those of platinum. Iron wires being used instead of 

 platinum, and a solution of potash for sulphuric acid, the secondary 

 current also appeared. Experiments with silvered copper wire, zinc, 

 and other metals, gave similar -results ; so that it is in the highest 

 degree probable that all metallic conductors have the property of being 

 electrically polarized. 



In the second of the above-mentioned memoirs (P. A. XLVII, 101) 

 Schonbein arrives at an explanation of the phenomenon. The most 

 important facts which lead to it are the following : 



1. Platinum wires or plates which, being placed for a greater or 

 less length of time in pure water, or in water with sulphuric or nitric 

 acid, hav^e served as electrodes, and are then heated to redness in a 

 spirit flame, lose entirely all their electro-motive power. 



2. If the positively polarized electrode, or that which has served as 

 a negative pole, be exposed but for a few moments to an atmosphere of 

 chlorine or bromine, the electro-motive force will be completely de- 

 stroyed ; the same result is also obtained by a longer immersion in 

 oxygen gas. 



3. A negatively polarized platinum wire loses its electro-motive 

 force if it be exposed a few seconds to an atmosphere of hydrogen. 



'4. By exposing positively or negativ^ely polarized platinum plates 

 to a gas which has no chemical action either on oxygen or hydrogen 



