6 MR. H. TOMLINSON ON THE INFLUENCE OP STRESS AND 



Expefriment V. 



The day after the last experiment had been made a fresh series of trials was 

 instituted with currents of various strengths. 



Remarks on Experiments I.- V. inclusive. 



It has been already noticed that when a large magnetising stress is used there is 

 but a slight increase in the internal friction, provided the magnetising current is not 

 interrupted or reversed during the trial, whilst Experiment IV. shows that if the 

 current be previously reversed a great number of times even this small increase 

 vanishes.* Accordingly, it may be said that under the conditions mentioned above 

 the internal friction is quite independent of any sustained magnetic stress which may 

 be acting on the vibrating wire. Similarly, there can be little doubt, the internal 

 friction of a torsionally vibrating wire would be entirely independent of the amount 

 of sustained statical torsional stress to which the metal might be at the same time 

 subjected, provided the wire had been previously vibrated torsionally a great number 

 of times. 



The torsional elasticity is also equally independent of even large sustained mag- 

 netising stress, for it may be observed that the mean value of the vibration-period 

 deduced from Experiment I. is for the magnetised iron 2'4745 seconds and for the 

 uumagnetised iron 2 '4767 seconds, whilst in Experiment I\ r . it is for the magnetised 

 iron 2'47865 seconds and for the unmagnetised iron 2'47860 seconds. Other experi- 



* If we take the last six trials of this experiment, we get for the logarithmic decrements, when the 

 magnetising solenoid is not excited, and when it is, the values '0009305 and '0009332 respectively ; the 

 difference between these two values lies within the limits of errors of observation. 



