248 Mr. H. Tomlinson on some 



in showing that repeated oscillation will reduce the internal 

 friction ; but they also show a very large influence to be 

 exerted by long rest, either with or without oscillation, and have 

 further proved that considerable diminution, both temporary 

 and permanent, can be produced by merely raising the 

 temperature of the wire to 100°C. Thus a well annealed 

 iron wire, when tested about ten minutes after suspension, 

 was found to have a logarithmic decrement due to the 

 internal friction of the metal of "003011, after one hour of 

 •001195, and after one day of '001078. After the last period 

 the friction became sensibly constant, and after four days was 

 found to be still the same ; the wire had apparently " accom- 

 modated " itself as far as possible. 



Great, however, as was the reduction of the internal friction 

 produced by oscillation and rest, the minimum had by no means 

 been reached ; for on repeatedly heating the wire to 100° C, 

 and then allowing it to cool, the logarithmic decrement rapidly 

 diminished, until after six days, on each of which the wire was 

 heated to 100°C, and then allowed to cool slowly, it became only 

 •000412, when further repetition of the above process ceased to 

 sensibly affect the friction. The greater part of the diminution 

 occurred after the first heating and cooling, but several repeti- 

 tions were necessary to produce the minimum mentioned above. 

 Still more marvellous is the temporary effect of a rise of 

 temperature not exceeding 100° C. on the internal friction of 

 annealed iron. A careful examination of the above specimen 

 at temperatures ranging between 0° C. and 100° C, revealed 

 the astonishing fact that, at a temperature of 98° C, the 

 logarithmic decrementwas only *000112, and was considerably 

 less than one fourth of its amount at 0°C * At 98° C. the 

 friction was a minimum, further rise of temperature resulting 

 in increase of the logarithmic decrement. It may perhaps 

 assist us in forming some notion of the very small amount of 

 internal friction in the above specimen of iron at 98° C, if we 

 estimate the number of vibrations which would be required 

 before the amplitude would be reduced to one half of its initial 

 value by molecular friction only : this number is nearly 3000. 

 It follows that if we could make the wire and its appendages 

 vibrate in vacuo, and maintain the temperature constantly at 

 98° C, with a vibration-period of ten seconds, more than eight 

 hours would elapse before an initial amplitude of 100 would 

 be reduced to 50. 



The internal friction of the wire when reduced to its 

 minimum by all the above-mentioned processes was only one 

 thirtieth of its original amount. 



* The temporary diminution of the internal friction of annealed iron 

 was shown at the meeting of the Society. 



