Effects due to Magnetization, 481 



liquid resistance in the field current. This change of resist- 

 ance was necessarily made more or less suddenly,, and the 

 deflexion experienced at each increase of resistance a not 

 very sudden throw toward reversal, in every respect the 

 same as had been repeatedly observed in the preliminary 

 experiments, and very different from the characteristic " pro- 

 tective throw," which is always sudden and in one direction. 



By simply varying the field current with care, as explained 

 above, the deflexion could be reversed again and again at 

 will, and could also be held at the zero of the scale, indicating 

 no current at all, as long as desired. When once the field 

 was entirely broken, the iron salts were released from the 

 control of the exposed pole, seriously disturbed by gravity, 

 and putting on the field again failed to reproduce the results 

 noted above. 



The only elements of difference in the two cases are, (a) 

 the magnetized condition of the metal, {b) the distribution of 

 the iron salts formed by the reaction. 



Although, as the curves indicate, the average electromotive 

 force with the magnetic field was much greater than in the 

 former case, yet this electromotive force is due to the difference 

 of action at the two exposed surfaces, and, as will be pointed 

 out later, the total amount of iron dissolved and passing into 

 solution in the two cases is probably not very different *« 

 Quantitative experiments are wanting on this point. 



The influence of the magnetized condition of the metal and 

 its magnitude is exhibited in the phenomenon of the " pro- 

 tective throw," which is always observed with apparatus 

 sufficiently delicate unless it is masked by other secondary 

 phenomena. 



Since the electrodes were embedded in hardened gelatine, 

 there could be no convection-currents in the liquid, and this 

 can be eliminated. Evidently the great difference in the 

 behaviour of the cell in the two experiments described is 

 principally due, either directly or indirectly, to the distribu- 

 tion of the iron salts formed by the reaction in the two cases. 



The principal time effects of the magnet were : — 



(a) To produce a higher potential at the point of greater 

 magnetization. 



(b) To increase the rate of change of the potential between 

 the electrodes and the absolute value of this potential dif- 

 ference. 



(c) It also appears from both curves that after a certain 

 distribution of iron salts is reached, further presence of the 

 same does not affect the permanency of the current established. 



* Fossati, Bolletino dell ' ' Elettricista , 1890. 



