70(5 



with the theoretical one. If we take 1200 for the magnetisation 

 reached by the iron, we get (the voliinie of tlic cylinder being 0,16 

 cm') /s=:192. By direct observation of tiie osciUations in liie aller- 

 naling field we found 



K = 0,533. 



As Q = 0,0065, 



it follows from (16) that 



|<r =0.0036. 



For a scale distance of 45 cm this gives for tlie donhie deviation 

 4|«| .45 = 0,65; as lias l)een said already, we have found 0,45 by 

 our experiments. 



As to this difference we must observe that the theoretical value 

 is an upper limit, as the magnetism does not change its sign in- 

 stantaneously. 



On account of the demagnetising influence of the free poles the 

 field in the coil must be rather strong if on its reversal the mag- 

 netisation is to take immediately a constant value in the new direction. 



§ 6. Determination of the phase. 



We have seen that the active couple differs a quarter of a period 

 in [)hase from the alternating nuxgnetisation. Further it follows from 

 § 3 that by comparing the phase of the effect (Pj with that of the 

 alternating current (P,) we shall be able to decide, whether the 

 electrons circulating round the iron molecules are really negative 

 ones. We have tried to effect this by proceeding in the following way. 



The single wire lamp used for the scale reading* was connected 

 with the main alternating current conductors in parallel with the 

 coil that contained the iron cylinder. If then we brought a perma- 

 nent magnet near the lamp, the incandescent wire was set into 

 motion by alternating electromagnetic forces, so that, besides the 

 oscillations due to the vibrations of the mirror, the image also 

 performed those that were caused by the motion of the wire. 



By observing whether the addition of this last vibration increased 

 or decreased the amplitude of the image, we could compare the 

 phase Pj with that of the new vibrations. Now this latter is deter- 

 mined by the phase of the glowing wire and this in its turn depends 

 on the phase of the current in it, whereas the difference between 

 this phase and P^ is determined by the self-induction of the coil. 

 It would therefore be possible to compare the phases P, and P,. 



Unfortunately, when our experiments had been brought to a con- 

 clusion and one of us had left Berlin it came out that a mistake 



