On the Effects of Changes of Temperature on Metal Wires. 193 



sidence is in each case greater at the higher temperature than at the 

 lower. 



It was observed by Lord Kelvin that increase of period as well as 

 increase of stretching force affected the rate of subsidence, these 

 effects being opposite. The effect of increase of stretching force 

 increased the rate of subsidence. The effects of increased mass of 

 vibrator given here are therefore mainly those due to increase of 

 pull in the wire. We are, however, arranging to alter the period 

 without altering the pull, and to alter the pull without changing the 

 period, by using suitable vibrators. 



There is one characteristic of these curves for commercial copper 

 which was shown also in the case of soft iron, but which does not 

 appear in the other experimental results. The falling off of amplitude 

 goes on very quickly in curves (3) and (4), and (5) and (6) in such a 

 way that the curves are almost straight lines, until the amplitude has 

 come down to only some 3 or 4 degrees, and then the subsidence 

 becomes comparatively slow. The curves for the 3 Ib. vibrator show 

 at the low temperature a logarithmic decrement increasing in the 

 ratio 27 to 60 as the amplitude falls from 80 to 24. At the higher 

 temperature the logarithmic decrement is practically constant. 



DIAGRAM IV(i). 



Copper (commercitAL). 



O 60 JOO ISO 200 



Diagram IV(&) shows subsidence at four temperatures which, taken 

 in the order in which the experiments were made, were 10'2, 51'1, 

 53'3, 78 - 4 C. In this diagram 150 divisions of abscissa represent 34. 



Diagram V() gives the rates of subsidence for pure electrolytic 

 copper at temperatures 23 - 2 and 92'1 with the 3 Ib. vibrator. Here 

 there is no sign of the change of character of the curves of subsidence 

 at low amplitudes which has just been noticed. The curve of subsi- 

 dence at the higher temperature is indeed nearly an exponential 

 curve at all amplitudes less than 20. The curve for the lower tem- 

 perature shows a logarithmic decrement at first somewhat quickly, 



p 2 



