394 



Scientific Proceedings, Royal Dublin Society. 



wire' ; and it has also been shown tliat the greatest damping of the torsional 

 oscillations in the wire takes place in a magnetic field of the same value.' 

 The magnetic field, therefore, employed in the present investigation was 

 2'8 c.g.s. units, whether continuous or alternating, unless otherwise stated. 



The effective length of the wire used was 226 cms., and of diameter 

 0"162 cms., that is a small No. 16; two different longitudinal loads were 

 employed for the tests on the pure iron wire, namely, 10* and 2 x 10' grammes 

 per sq. cm., and the wire was tested in two different physical states: (1) in 

 the condition in which it was received from tlie manufacturer, (2) after being 

 made as soft as possible. Alternating magnetic fields of frequencies less than 

 50 per second were tried, but the results are not here recorded, because the 

 differences between the damping curves with direct and alternating magnetic 

 fields are much less for iron than for nickel. 



A pure iron wire was taken in the physical state in which it came from 

 the manufacturer, and after having its surface cleaned with emery, and its 

 rigidity measured,' it was placed in the solenoid, and the subsidence of 

 torsional oscillation observed when it was surrounded by magnetic fields of 

 value 2'8 units, both D. C. (direct current) and A. C. (alternating current), 

 and also when it was subjected to two different loads. 



The results are shown in Table I. 



Table I. 

 Rigidity == 808 x 10° grammes per sq. cm. 



1 Sclent. Proc. Eoy. Dub. Soc, vol. xii, 1910, No. 36, p. 484. 



2 Scient. Proc. Roy. Dub. Soc, vol. xiii, 1911, No. 3, p. 41. 



3 Scient. Proc. Hoy. Dub. Soc, vol. xii, 1910, No. 36, p. 481. 



