522 



Scientific Proceedings, Royal Dublin Society. 



in the subsidence experiments or the steady deflection in the fatigue experi- 

 ments was placed at a distance of 167 cms. from the plane mirror on the 

 vibrator or load on the end of the wire. The maximum deflection of the 

 light-spot which was used in the subsidence experiments was at the distance 

 marked 300 on the scale, which corresponded to a torsion or twist of the 

 lower end of the wire equal to an angle of about 5° 10' on eacli side of the 

 zero. 



In the course of the experiments on " fatigue," the direct current through 

 the wire was in each case equal to one ampere. 



The wire first tested was in the physical state in which it was received 

 from the manufacturer, and when measured it had a simple rigidity of about 

 810 X 10* grammes per sq. centimetre. When it was placed in the solenoid 

 with the load at its lower end, a deflection or twist was produced of only one 

 millimetre on the scale when the proper currents were sent round the solenoid 

 and through the wii-e ; the wire therefore in its original state of rigidity 

 could not be tested for fatigue. 



It was, however, tested for the subsidence of torsional oscillations, and, for 

 comparison, observations were made when the wire was in two longitudinal 

 magnetic fields, viz. the vertical component of tlie Earth's field and a field 

 of 20 c.g.s. units, and then when it was in an alternating magnetic field 

 of 20 c.g.s, units, at three different values of the frequency. 



The more significant of the results are set out in Table I, and are sufficient 

 to show what the trend of the curves would be if the results were plotted 

 with the number of vibrations as abscissae, and the corresponding values of 

 tlie amplitude of oscillation as ordiuates. 



Table I. 



The numbers in the tables under the letters D. 0. were obtained when 

 direct longitudinal magnetic fields were round the wire, and those under the 



