KR. BIRKELAND. M.-N. Kl. 



I will now describe another inducting .system that can more practically 

 be introduced into a circuit through which a current is passing, in order to 

 facilitate its breaking off. In the application of the system mentioned 

 above, a large iron core was set in violent motion ; in the following 

 arrangement, such motion will be avoided. 



A large, annular core of laminated iron is first covered with some 

 layers constituting a continuous primary coil. Outside this are placed a 

 great number of .segments of separate secondary coils, as shown in fig. 

 2 a. The primary coil may also be laid in numerous segments connected 

 in a série, in which case one or more of the secondary segments must 

 be placed alternately with the former, as shown in fig. 2b. 



2 a. 2 b. 



Fie. 2. 



Each secondary segment is connected with its proper contact, and 

 all these small contacts are mounted into a ring on the edge of a circular 

 disc of ebonite. Through these contacts, all the secondary segments are 

 connected with a source of current, in such a way that the iron ring 

 -seen from above, is magnetised, say with the hands of a watch. 



The ebonite plate can be lifted straight up, so as to break off all 

 the contacts simultaneously. In the centre of the ebonite plate, there 

 IS a principal contact, closing the primary circuit; and this principal 

 contact is also opened almost simultaneously with the numerous small 

 ones, when the ebonite plate is raised. The primary coil is wound in 

 such a way as to make the primary current magnetise the iron core in 

 a direction reverse to that of the secondary current, the reverse, in casu, to 

 that in which the hands of a clock move; but the magnetising force of 

 the primary current is supposed to equalise the magnetising force of the 

 secondary current. When both the primary and the secondary coil convey a 

 current, the iron core becomes in consequence non-magnetic, and the 

 inducting system in question has a minimum of self-induction. 



The dimensions of the secondary coil should be such that on each 

 of the small secondary contacts, which should be very numerous, at 

 most lo ampères at lo volts arc broken, and a considerably smaller 



