Otf THE MODULUS OP TORSfOtfAL RtGlDITY OF METAL WlfcES. 27 



The values of the logarithmic decrements obtained at the various temperatures are 

 given in Table IV. Each is, in general, the mean of several observations. 



TABLE IV. Soft Iron Wire. 



From the numbers in the above table it will be seen that the logarithmic 

 decrement decreases with increasing temperature. This is just the opposite to what 

 happened in the case of copper. As a rule repeated heatings diminished the value of 

 the logarithmic decrement. This shows most clearly at the ordinary temperature, 

 where the value of the logarithmic decrement is largest. It is peculiar that after 

 passing 100C. the value of the logarithmic decrement has attained a minimum and 

 begins to increase with increasing temperature. There is no doubt about this, for 

 a large number of observations were taken at 100 C. and at 126C., some of those at 

 100C. being taken before and some after those at 126C. This result had also been 

 obtained with another iron wire on which I had previously experimented, using the 

 old form of heating jacket. Another curious point is that the first heating increased 

 the value of the logarithmic decrement at ordinary temperatures, while all subsequent 

 heatings diminished it. This result was also obtained with the first iron wire, and 

 with the copper wire as can be seen in Table II. 



In Diagram II. a curve is drawn through the value of the logarithmic decrement 

 from the first observation at each temperature. 



When all the observations for finding the rigidity were finished, I investigated 

 whether the time of vibration and the logarithmic decrement varied with the 

 amplitude of swiug so long as this was small. The following two results were the 

 means of several determinations : 



E 2 



