Brown — Mechanical Stress and Magnetisation of Nickel. 43 



The values obtained in one set of observations, from an initial amplitude 

 of 90°, and for magnetic fields up to 60 c.g.s. units, are given in Table V., and 

 six of them are shown as curves in fig-. 5. 



20 



50 40 50 60 



Fig. 0. — Number of Vibrations. 



In fig. 5, the number of vibrations attained from the initial amplitude of 

 127 divisions on the scale or 90° are plotted as abseissse, and as ordinates the 

 corresponding values of the amplitude ; the number at the right-hand end of 

 each curve indicates the value of the longitudinal magnetic field that was 

 round the wire when it was being tested. These curves show that the internal 

 friction in the nickel wire is increased and then decreased by the presence of a 

 magnetic field, but in a rather curious manner when high initial amplitudes 

 are used. 



With no magnetic field, and with a field of five units round the wire, the 

 slope of each curve is quite smooth and regular ; but when a magnetic field of 

 twelve units is round it, there is a slight flexure in the curve about tlie fifth 

 vibration from the start ; the magnitude of this flexure is increased with a field 

 of thirty units, and still further increased with a field of fifty units, and then 

 diminished with a field of sixty units ; the position of the flexure being sliifted 



SCIENT. PROO. R.D.S., TOL. XIII., KO. m. 



