106 



Mr. Herbert Tomlinson 



The logarithmic decrement due to internal friction was 

 determined in the first instance before the wire had been 

 heated at all, and proved to be 



•002203*. 

 The wire was now heated to the highest temperature recorded 

 in this experiment, and was maintained for about half an hour 

 at this temperature, being all the time kept in torsional oscil- 

 lation ; it was then allowed to cool, and immediately after 

 cooling was again tested. The logarithmic decrement now 

 proved to be -0193G7. 



After a rest of one hour the logarithmic decrement had con- 

 siderably diminished, and finally fell to 



•00977. 



Lastly, the wire was again raised to the previous high tem- 

 perature, and as soon as the logarithmic decrement and 

 vibration-period had become sensibly constant f their values 

 were registered. The temperature was then lowered by put- 

 ting resistance into the battery-circuit, and a fresh set of 

 observations was taken, and so on, until eventually the tem- 

 perature of the wire was reduced to that of the room, when 

 the logarithmic decrement proved to be sensibly the same as 

 the one last recorded. The results of the observations, which 

 extended over a period of several days, are given in the 

 following table : — 



Time of 

 vibration, 

 in seconds. 



Modulus oi 

 torsional 

 elasticity, 

 in grammes 

 per square 

 centim. 



Tempera- 

 ture, in 

 degrees 

 Centigrade, 

 t. 



Logarithmic 

 decrement 

 due to in- 

 ternal fric- 

 tion, \. 



Difference 



between 

 consecutive 

 tempera- 

 tures, At. 



Difference 



between 



consecutive 



values'of X, 



AX. 



AX : At. 



1-523 



726-6 X10 6 



20 



•00977 









1573 



681-1 



220 



•01805 



200 



•00828 



000041 



1-700 



583-2 



543 



■05033 



323 



03228 



•000100 



2-020 



4131 



930 



•09634 



387 



04601 



■000119 



2-100 



382-2 



989 



•11216 



59 



•01582 



•000268 



2-486 



272-7 



1181 



•20950 



192 



09734 



•000507 



2-600 



249-4 



1220 



•19680 



39 







* The wire was unannealed, otherwise the logarithmic decrement 

 would have been probably less than half of the amount here given. 



f Any change of temperature, whether in the direction of increase or 

 decrease, is always attended in the first instance with a larger internal 

 friction than that which ultimately prevails when the vibrations are con- 

 tinued long enough. 



