STRAIN ON THE PHYSICAL PROPERTIES OP MATTER. 



3 



nearly constant throughout its entire length. In order to maintain the temperature 

 constant, water from a large pail was made to flow into the annular space through 

 the tube D, and out through the tube D 2 during the whole of the period of experi- 

 menting. The magnetising solenoid was actuated by ten GKOVE'S cells, the current 

 from which passed through a resistance-box, a tangent galvanometer, and a commu- 

 tator (not shown in the figure). The precautions adopted in the previous experi- 

 ments were here reproduced, care being taken that the amplitude of the vibrations 

 should be well within the limits of elasticity. 



Experiment I. 



An annealed iron wire, 100 centims. long and '1 centim. in diameter. The current 

 was always sent through the magnetising solenoid in the same direction,* and at 

 least a hundred vibrations were allowed to take place, both when the solenoid was 

 excited and when it was not, before the actual testing began. The experiment was 

 carried on for two days for about six hours on each day, and the numbers given below 

 for the logarithmic decrements and times of vibration are in each case the mean 

 values resulting from 400 vibrations, first without excitation of the magnetizing 

 solenoid, then with, then without, and so on. 



First Day. 

 MAGNETISING solenoid not excited. 



* Except in the fourth trial, when it was reversed for a few seconds by accident. 



t The damping due to the resistance of the air has in all the experiments been calculated in the 

 manner described in ' Phil. Trans.,' 1886 (vol. 177, Part II.). 



{ The current was in this trial put on, in the first instance, in the wrong direction, but was afterwards 

 reversed while the trial was still going on ; this, no doubt, accounts for the logarithmic decrement being 

 larger than in the other trials. 



B 2 



