/VVvVivW 



the Torsion of a Wire by Change of Temperature. 163 



by the changes in the position of rest, and they are not of 

 great accuracy or consistency; but there can be no doubt that 

 the course of the values is as above described. 



It only remains to suggest what may 

 be possible in the way of explanation of 

 these phenomena. It appears to me 

 that the only way of throwing any light 

 on them is to imagine a mechanism 

 capable of producing angular changes 

 similar to those in question under the 

 influence of changes of temperature. 



A B are materials differently expan- 

 sible by heat, capable of shifting, but 

 with difficulty, through the clamp which 

 binds them together. 



Suppose C to be free between D and 

 E; then any change of temperature will 

 cause C to shift its position between D 

 and E, and the pinion F will be turned 

 round by the racks between which it 

 lies. As soon as C comes up either 

 against D or E the rotation of F is 

 stopped, and the bars are compelled to 

 shift in the clamp, if there is further 

 change of temperature. 



This arrangement exactly reproduces 

 the typical changes observed in the pre- 

 sent experiments. It is intended to 

 serve the purpose of a formula. 



The suggestion which we obtain from 

 the above mechanism is that of loose 

 contact between the parts involved, in 

 this case probably between the molecules 

 of the metal. As these peculiarities 

 appear to originate in the extension of 

 the wire by the suspended weight, it is 

 possible that a partial separation of the 

 molecules involving loose contact may 

 arise out of this extension. 



In any such case the molecules would 

 bed against each other at the opposite 

 parts of the loose contact, under the 

 conditions which would give rise to either of the limiting 

 elongations in the above experiments. The whole framework 

 would be much stiffer when the loose contacts were thus 

 bedded together than when they were free. In this way it 

 would be possible to account for the increased values of the 



M2 



LS 



