759 



Cbarlottenburg kindly procured me. The magnetized electrode con- 

 sisted of a circular plate, which was of the same size as the pole 

 plane of the electromagnet, and was rigidly fastened to it, a glass 

 plate serving as isolation. The other electrode was outside the field. 

 The concentration of the used solution of ferrosulphate was generally 

 57o- The results obtained with this may be summarized as follows. 

 On excitation of the magnetic field I ahvays obtained a current in 

 the sense as the theory requires. The extent of the obtained effect 

 differed, however, greatly from the theoretical value ; the measured 

 potential differences were, namely, between the strengths of the 

 field and about 20.000 Gauss 10 or 20 times as great as the for- 

 mula would require. At first the course was about proportional to 

 the second power of the strength of the field, the effect reaching a 

 value of 6.3 X 10—* Volts at about 16000 Gauss, which did not 

 change on further strengthening of the field. If the used solutions 

 were neutral, the effect remained pretty well constant after excita- 

 tion of the field. On the other hand for acid solutions (which con- 

 tained only very little free acid) a diminution and a reversal of the 

 effect soon took place, till a value was reached, about ten times as 

 great as the first effect after the excitation of the field. It is remark- 

 able that Rowland and Bell also always found sueh a reversal, 

 whereas Squier found that above a certain strength of field the effect 

 no longer increased, which is in agreement with what I observed. 

 Another phenomenon that I regularly observed was the increase of 

 the resistance of the solution as it was longer in the tube. At last this 

 resistance can reach a value of some hundreds of thousands of ohms. 

 Besides I made experiments with nickel. The electrodes were of 

 so-called "Rein nickel" from the firm Kahlbaum; as electrolyte 

 generally a 5 "/o solution of nickel sulphate was used. No effect, 

 however, was observed with certainty, so long as the solution was 

 neutral. Probably there was an effect in the sense required by the 

 theory, but about five times smaller than for iron, which would 

 therefore harmonize better with the theory. It was, however, impos- 

 sible to obtain certainty in this respect, as the resistance of the 

 solution soon became exceedingl}^ great, even up to more than 

 10" Si ; moreover the zero position wa^ very variable, much more 

 so than was the case for iron. It is peculiar that the large resistance 

 only consisted for very small electromotive forces ; if on the other 

 hand the latter was a few volts, the resistance became only a few 

 thousands of ohms. For solutions of nickel sulphate greatly acidified 

 with sulphuric acid no other effect was found than in neutral 

 solutions ; there was no question of a reversal here. 



