38 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
18. The loss of torsional rigidity mentioned in 16 is more sensible proportionally 
with large arcs of vibration than with small ones. 
19. Continual vibrating through large arcs has a similar effect on the torsional 
rigidity to that produced on “ Young’s modulus ” by heavy loading and unloading. 
20. The density of a wire is very little altered by permanent extension, even if the 
latter be carried to the extent of breaking the wire. 
21. The values of “ Young’s modulus ” obtained for the different metals are, roughly 
speaking, inversely proportional to the seventh powers of the mean distances between 
adjacent molecules in these metals. 
22. The torsional rigidity of copper and iron wires seems to be temporarily decreased 
by the passage of a powerful electric current through the wires. 
23. The torsional rigidity of iron wire seems to be temporarily diminished when the 
wire is subjected to a powerful longitudinal magnetizing force. 
24. The effects mentioned in 22 and 23 are apparently independent of any change 
produced by the electric current or the magnetizing force of the temperature of the 
wires. 
25. There are, in every well-annealed wire, two critical points at which sudden 
changes take place in the ratio of the permanent extension produced by longitudinal 
stress which is gradually increased in amount and the magnitude of the stress. 
