1299 
phases. The observed phenomena can only be understood by assuming 
that besides 4 and u there is another vibration (1 and 3), which 
appears when 4 and mw neutralize each other. 
(As, on account of the self-induction, the actions giving rise to 
A and u do not begin quite simultaneously, this is a cause for a 
small difference in phase. But this is just what we have called 3, 
so that it has been taken into account.) 
These experiments were carried out in the physical laboratory of 
the Trrrer-Institute at Haarlem. I readily express my thanks to the 
Directors of the Institute and to the Curator of the Laboratory for 
their so kindly putting at my disposal the necessary apparatus. 
Physics. — “On the injluence of alternating currents of decreasing 
intensity on the magnetisation of tron.” By Dr. G. J. Erras. 
(Communicated by Prof. Dr. H. A. Lorentz). 
(Communicated in the meeting of Jan. 29, 1916.) 
1. It is generally supposed that magnetized iron is quite demagnet- 
ized when placed in a magnetic field of alternating direction, the 
intensity of which decreases to zero. It is however desirable to inves- 
tigate this process more closely. As we must then necessarily use 
a definite representation about the magnetic state, we shall suppose, 
referring to the considerations of Weiss, that iron consists of a very 
great number of “elementary crystals’. Of each crystal we shall sup- 
pose that its magnetic moment can be directed along one definite 
line only either in positive or in negative sense. We shall neglect 
the mutual actions of the neighbouring erystals. Further we shall 
idealise the case by supposing that there exists “complete” hysteresis, 
so that all magnetic moments keep their direction, when the 
magnetizing force has vanished. 
In unmagnetized state the magnetic moments are equally distri- 
buted over all direetions,-so that the resulting moment of the iron 
is zero. Let us now suppose that an external magnetic force H is 
working and that a magnetic force 4 in a sense opposite to that of 
the magnetic moment of an elementary crystal is needed to let this 
moment change its direction. Then all those magnetic moments that 
h 
are lying within a cone with a top equal to 2 are cos = will do so 
and the corresponding elementary erystals contribute to the magne- 
tisation of the iron. 
84 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
