Bkown — Subsidence of Oscillations of Iron Wires and Alloys. 399 



S FICTION II. 

 Iron Alloj/s. 



The alloy of iron that the present writer wished particularly to test was 

 one whose trade name is Stallorj, a silicon iron with about 3'4 percent, of 

 silicon, and the principal physical properties of which were investigated in 

 the Royal College of Science some years ago/ 



The material Stall oy could not be conveniently obtained in the form of 

 wire No. 16, which is the most useful size for these experiments, so, for com- 

 parison, size No. 20 wires were procured of Stalloy and S.C.I. (Swedish 

 charcoal iron), and put through tests similar to those already described. The 

 two wires were tested under exactly the same conditions as to length, 

 diameter, load, and magnetic fields both D.C. (direct current) and A.C. 

 (alternating current). The longitudinal load on each was 1 x 10' grammes 

 per sq. cm., the magnetic fields 2'8 c.g.s. imits, and the distance from the 

 mirror on the vibrator to the scale 167 cms. 



The wire S.O.I, in the physical state in which it was received from the 

 manufacturer was too hard to be magnetised sufficiently by the field of 2'8 

 units, to obtain a curve of fatigue.' In the damping curve, or curve 

 showing the subsidence of torsional oscillations, the amplitude of oscillation 

 fell from 300 on the scale to 180 with the D.C. magnetic field, and 

 from 300 to 177 with the A.C. field, for seventy complete vibrations in 

 each case. 



The wire was then taken down and heated three times to a bright red 

 heat by means of a Bunsen flame, and when cool and cleaned it was again 

 put into the solenoid, and the damping curves obtained for both D.C. and 

 A.C. magnetic fields. The results are shown in Table IV. The maximum 

 fatigue of the wire in this softer state was found to be 0'22, and it took place 

 in 30 minutes' application of the A.C. magnetic field. The silicon iron wire, 

 stalloy, in the physical state in which it was received from the manufacturer, 

 was not so hard magnetically as the wire S.C.I., and when put through tests 

 similar to those applied to S.O.I., it was found that in the damping curves 

 the amplitude of oscillation in the D.C. field fell from 300 to 251, and 

 in the A.C. field from 300 to 237 for seventy complete vibrations in 

 each case. 



Iq tliis comparatively hard state the wire showed fatigue which had 

 a maximum value of 0"2, after 25 minutes' application of the A.C. 



' See references to Vestalin below. 



» Scient. Proc. Roy. Dub. Soc, vol. xir, 1915, No. 26, p. 336. 



