[ 393 ] 



XXXII. 



THE SUBSIDENCE OP TORSIONAL OSCILLATIONS OP lEON 

 WIRES AND ALLOTS WHEN SUBJECTED TO THE 

 INPLUENCE OP ALTERNATING MAGNETIC PIELDS OF 

 FREQUENCY 50 PER SECOND. 



By W. brown, B.Sc, 

 Professor of Applied Physics, Royal College of Science for Ireland, Dublin. 



[Read January 26. Published Maech 5, 1915.] 



Section I. 



Iron Wires. 



About a year ago there was brought before this Society the results of some 

 experiments on the subsidence of torsional oscillations in nickel wires when 

 they were subjected to the influence of alternating magnetic fields of 

 frequencies from 20 to 140 per second.' The present commvmication gives 

 some results with iron wires and a few alloys, with alternating magnetic 

 fields of frequencies 60 per second only. At present, the alternating currents 

 available for producing magnetic fields of frequency higher than 50 per 

 second do not give pure sine curves when analysed by means of an oscillo- 

 graph, and experiments with alternating fields of frequencies up to 240 per 

 second liave been held over until a machine has been installed for this work 

 which will give high frequency currents tlie graphs of which are practically 

 pure sine curves. 



For a detailed description of the apparatus employed, and of the method 

 of experiment, I would refer to page 216 of the paper mentioned above. The 

 only important changes introduced since that time are : — (1) the longitudinal 

 loads on the end of the wire under test are now shallow cylinders, which can 

 be firmly clamped by means of lock-nuts ; (2) instead of the wire being made 

 to oscillate round its own axis by an electrical metliod, it is now done 

 by means of two properly timed simultaueous pufl^s of air, which strike 

 tangentially on the sides of the vibrator. 



It has been shown for iron wires, that the magnetic field which must be 

 round the wire in order to get the maximum twist of the free end is inde- 

 pendent of the load on the end of the wire for a given current through the 



1 Scient. Proc. Eoy. Dub. Soc., vol. xiv, 19U, No. U, p. 215. 



SCLENT. PROC, K.D.S., VOL. XIV., NO. XXXII, 



