40 DR. F. HORTON ON THE EFFECTS OF CHANGES OF TEMPERATURE 



The value of the rigidity modulus at 15 C. was found to be n l5 = 1'4960 X 10" 

 dynes per sq. centim. and the " temperature coefficient" ft = '005942. 



Some experiments were also made with another pure tin wire which had not been 

 previously annealed. The range of temperature employed in this case was only 

 34 C. The value found for the rigidity modulus at 15 C. was n ]5 = T8715 X 10 11 

 dynes per sq. centim. and for the " temperature coefficient " ft = '00385. The 

 rigidity of tin is thus lessened by annealing. The " temperature coefficient " is much 

 the smaller in the case of the unannealed wire, but the alteration in the rigidity 

 modulus per 1 rise of temperature is more nearly equal in the two cases. 



The values of the logarithmic decrements of the amplitudes of oscillation obtained 

 during the experiments with the annealed wire showed an increase in the logarithmic 

 decrement with the temperature, and also a continual diminution with time. 



Observations of the logarithmic decrement of the oscillations of the unannealed tin 

 wire were made, and the results showed that the rate of increase of the logarithmic 

 decrement with temperature was much greater than in the case of the annealed wire. 

 The heating of the unannealed wire greatly reduced the value of the logarithmic 

 decrement at the ordinary laboratory temperature. 



Some observations on the effect of increased amplitude of vibration on the 

 logarithmic decrement gave very irregular results, complicated by the fact that the 

 logarithmic decrement of a constant amplitude diminished as time went on. The 

 observations showed that the logarithmic decrement increased with the amplitude of 

 oscillation, but in a very irregular manner. 



Lead. 



The wires used were drawn down from a strip cut from a sheet of lead. In order to 

 try to avoid the complications caused by the wire elongating under the slight tension 

 to which it has to be subjected, series of observations at different temperatures were 

 taken all on the same day. 



Observations were first taken with an unannealed lead wire, and it was found that 

 the rigidity increased very considerably as time went on, especially at the higher 

 temperatures. The rigidity-temperature curves obtained on different days were very 

 similar, indicating that the alteration of rigidity with temperature was practically 

 constant, although the absolute value increased as time went on. A specimen of the 

 curves obtained is given in Diagram VIII. 



The value of the rigidity modulus at 15 C. is n, 5 =7'505 X 10 10 dynes per sq. centim. 

 The mean value of the decrease per 1 rise of temperature at 15 C. was '0225 X 10 10 

 dynes per sq. centim., from which the "temperature coefficient " /3 = '00300. 



The logarithmic decrement of the amplitude of the torsional oscillations increased 

 with the temperature, but this effect was complicated by a very considerable decrease 

 iu the value with time. The results, however, showed that the rate of increase was 



