32 



Scientific Proceedings, Royal Dublin Society. 



The smallest load, 0-016 x 10' grammes per square centimetre, was 

 obtained by means of an aluminium tube with a mirror attaclied, and the 

 mao-netie field in whieli tlie maximum twist occurred with this load was found 

 to be 10'3 units. ^ 



In all the seven cases the cyclic curves were plotted to the scale in which 

 two centimetres represented one amj^ere on the axis of abscissae, and on the 

 axis of ordinates one centimetre represented ten divisions (mm.) of deflection 

 on the scale ; the total area of each curve was tlien measured in square 

 centimetres. The results are given in Table II. 



Table II. 



From Table II. if we plot the values in the first column on tlie axis of 

 abscissse, and on the axis of ordinates the corresponding values in the third 

 column, it will be found that tlie ^vsi five points lie in a straight line with a 

 rapidly rising slope, and the last three points lie also in a straight line which 

 lias a slowly falling slope. That is, the effect of increasing the load on the 

 wire is seen to reach a maximum with the load of 4 x lO'^ grammes per 

 square centimetre, as is also less clearly shown in fig. 1, p. 31. 



The Subsidence of Torsional Yibuations in Nickel and Ikon Wires 

 when subjected to the action of longitudinal magnetic flelds. 



Section 1. — Nickel Wire. 



It seems evident tliat the internal viscosity of a nickel wire is the 

 important factor in determining the maximum twist of the free end of a 



Scient. Proc. Roy. Dub. Soc, vol. xii., No. 37, p. 507, 



