32 Mr. W. Sutherland on a 



It next appeared in a similar manner that the law of 

 variation of Young's modulus of elasticity with temperature 

 is nearly the same for all metals, and nearly, though not 

 quite, as simple as that for rigidity. 



As these results amounted to an experimental proof that 

 rigidity (and elasticity generally) is essentially a kinetic 

 phenomenon I was encouraged to proceed with a kinetic 

 theory of solids, which had been in view when the experi- 

 mental inquiry was undertaken. 



The present paper will be divided into two parts : — 

 Experimental Introduction and Theory. 



Experimental Introduction. 



This will be divided into two parts, Rigidity and Young's 

 Modulus, in which the matter will be taken in the following- 

 order : — first, an account of my own experiments on the effect 

 of temperature on elasticity ; second, a compilation of all 

 available data on the same subject ; third, a compilation of 

 all the available data as to the absolute values of Rigidity and 

 Young's Modulus at about 15° C. ; and fourth, establishment 

 of the general law connecting these elastic constants with 

 temperature, and determination of their values at absolute 

 zero. 



Rigidity. 



1. Experiments. — -The variation of rigidity with tempera- 

 ture has been worked at by Napiersky, Kohlrausch, Pisati, 

 and Tomlinson ; but these experimenters have almost confined 

 their attention to the nobler metals with high melting-points. 

 As I expected that in the case of the metals with low melting- 

 points the law of variation would be easier to discover, it was 

 necessary to make a study of these metals. 



I used the torsional method of measuring rigidity both in 

 its static and kinetic form, and found the two forms to give 

 agreeing results ; but as the static proved less accurate, I will 

 hot waste space by giving its results here. The kinetic 

 method was worked in the usual manner. The metal to be 

 experimented on was taken in the form of a wire, with a 

 cylindrical vibrator of thin sheet iron soldered to one end, and 

 a strip of thin iron to the other by means of which it could 

 be clamped. As chamber in which to produce variations of 

 temperature, a wooden box about 65 centim. by 20 by 27 was 

 taken and fixed with its long edge vertical. The top and 

 bottom had a hole bored at each middle point to let the wire 

 pass through freely. The iron strip was clamped to the top 

 of the box, and the vibrator either swung just outside or inside 



