Physics. — “The Mechanism of the Automatic Current Interrupter’’. 
By Prof. J. K. A. WeRTHEIM SALOMONSON. 
(Communicated at the meeting of November 27, 1920). 
~The mechanism of the automatic current interrupter as represented 
by Hermnortz’s tuningfork interrupter, by Nurrrr-Wacnur’s hammer- 
break, and by the ordinary electric bell, has not yet been explained 
in an entirely satisfactory way. Lord Rarreien was the first to give 
an explanation, without, however, entering into details. Later on 
its mechanism was studied by Lippmann, Dvorak, Guinier, Bovassr 
and others although no new points of view were opened. In this 
paper | intend to submit a few considerations on this subject, prin- 
cipally based on a research into the attraction by the electromagnet 
on the armature during the working of the apparatus. As an indi- 
cator for the attraction I used the number of lines of force passing 
through the armature at each moment. These were measured by an 
oscillographic method. This might have been done by the new 
ABRAHAM-rheograph, but as I did not possess this instrument | 
employed Dreuisnr’s method, described in the Physikalische Zeit- 
schrift 1910, p. 513. The results of this method were compared 
with those obtained by a new method, which I shall describe in 
an appendix to this paper. 
The interrupter used in my experiments has a horizontal horse- 
shoe magnet. The cores turned from a solid bar of swedish iron 
completely bored and slit lengthways, have a length of 5 cm and 
a diameter of 1 cm. They are screwed at a distance of 3.2 cm 
from each other into a yoke of 1.4 cm?’ transverse section, and are 
each wound with 200 turns of well insulated copper wire of 1.2 ohm 
resistance each. The armature measured 1.2 X 0.75 « 4.4 em. It is 
screwed to a strong steel spring of 0.12 « 1.0 em. with a free 
length of 1.3 em. Into the other end of the armature a brass bar 
0.4 cm. in diameter and 5 em. in length was fixed, on which, if 
desired, a small copper weight could be screwed. It was generally 
used without weight and then made about 47 complete vibrations 
per second, the platinum contact being so adjusted as to make and 
break the current during one half of the periodic time. The arma- 
