504 



Scientific Prnceeclirif/s, Boijal Dtihlin Societil- 



These results exhibit several peculiarities and differences from those 

 obtained with iron wires in the same physical state and when tested under 

 the same conditions. 



It is well known that the twist produced in the free end of a nickel wire 

 is in the opposite direction to that produced in an iron wire when tested in 

 the same way' ; also that the maximum twist in iron takes place in the same 

 longitudinal magnetic field whatever the load on the wire may be, within 

 certain limits, and that the curve relating the longitudinal magnetic field 

 round the iron wive and the twist of its free end is lower the greater the load 

 on the end of the wire.^ 



Magnetic Field H. 

 Fig. 1. — "^S^ire of constant temper Ho, find under three different loads. 



One set of results for nickel wire is shown as curves in fig. 1 — that is, 

 for the temper or hardness Ho from Table II, where the abseissse are the 

 values of the longitudinal magnetic field round the wire, and the ordinates 

 the corresponding values of the twist of the free end of the wire expressed in 

 millimetres on the scale. Taking the curves in fig. 1 in order before they 

 cross one another, the top or left-hand curve is that obtained with the small 

 load on the wire, the lower or right-hand curve that obtained when the high 

 load was on, and the middle curve that obtained with the intermediate load 

 of 1'5 X 10* grammes per sq. cm on the wire. 



' Knott, Tran.s. Roy. Soc. Eiiin., vol. xxxii. 



■-■ Scieiit. Proc, Roy. Dub. Soc, vol. lii., No. 36, p. 484, 



