Effects due to Magnetization. 483 



stationary tremor of the needle at the instant of its starting 

 on the, " concentration throw." This latter, though called 

 a " throw," can be made to vary from an extremely slow 

 continuous movement of the galvanometer deflexion, as in 

 experiment B already described, to a comparatively rapid 

 deflexion at the instant of making the magnet. 



By using simply a dilute nitric-acid solution with no gela- 

 tine, and inserting a thick piece of glass between the 

 electrodes, the concentration effect was delayed enough to 

 allow the " protective throw " to first appear, with consider- 

 able iron salts in the solution; and on making the field both 

 effects were observed as described above. 



It now appears that the reversal of the current, uniformly 

 observed in the experiments of Messrs. Rowland and Bell, 

 was but a form of the " concentration throw " mentioned 

 above, and that we can regard the substitution of the hardened 

 acidulated gelatine for the dilute acid as merely separating these 

 effects, so that the former can be studied by itself ; in other 

 words, the reversal of the current would have occurred just 

 the same after a sufficient time had elapsed. 



Turning to the experiments of Drs. Gross and Andrews, 

 they employed but one magnetized electrode, which was not 

 pointed. In this case the nature of the magnetic field at the 

 two exposed surfaces would be very much more nearly the 

 same than when a pointed electrode is employed. This 

 arrangement is not, therefore, suited to bring out the delicate 

 "protective throw," and it is not surprising that the concen- 

 tration effect was the prominent feature observed. 



We have now a complete reconciliation of the directly 

 opposite results referred to in the introduction. The "pro- 

 tective throw " is due to the actual attraction of the magnet 

 for the iron, and is always in the direction to protect the 

 more strongly magnetized parts ; while the " concentration 

 throw " is always in the opposite direction, and depends upon 

 the distribution of the iron salts present in the solution, and 

 the convection-currents in the liquid. The concentration of 

 the products of the reaction about the point would tend to 

 produce a ferrous reaction instead of a ferric, and experiment 

 shows that a higher electromotive force is obtained with cells 

 in which a ferrous reaction takes place than with those in 

 which a ferric reaction occurs ; and this change in the 

 character of the reaction produced by the concentration prob- 

 ably accounts, at least in part, for the increased electro- 

 motive force at the point. 





