AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
27 
Remarks on the above experiments. 
It appears from Experiments XIV.-XVIII. inclusive (1) that the loss of rigidity 
produced by twisting or stretching a wire beyond the limits of elasticity, is partly 
diminished by rest; (2) that the loss is more sensible with large arcs of vibration 
than with small ones; and (3) that the influence of rest is more apparent in the case 
of large vibrations than in that of small ones. 
Experiment XIX. shows that continual vibrating through large arcs has a similar 
effect on the rigidity to that produced on the longitudinal elasticity by heavily loading 
and unloading, the time of vibration through large arcs being by the former process 
made less, just as the temporary elongations caused by heavy loads are diminished by 
the latter. 
Finally, Experiment XX. shows that in the case of a wire possessing great coercive 
force, the effect of vibrating through a large arc for several minutes actually makes 
temporarily the rigidity, as determined from such vibrations, greater than that deter¬ 
mined from smaller vibrations : an effect analogous to that produced by leaving a wire 
heavily weighted for some time, when, as we have seen, the temporary effect on the 
length of large loads is less in proportion than of small ones. 
We thus see that the effect of permanent torsion on the torsional rigidity is similar 
in every respect to the effect of longitudinal extension on the value ol Young’s 
modulus.” 
Iron, aluminium, copper, and silver are the only metals which have, as yet, been 
tested in the above-mentioned manner, and iron, as before, is conspicuous for the large 
influence on it of continued rest. 
In Table II. will be found embodied the results obtained in the case of each 
substance for the modulus of rigidity and “ Young’s modulus,” together with some 
other data which are further supplemented in Table III.* 
* For observations on the moduli of elasticity of nickel and carbon at the ordinary temperature of tne 
room, and of iron, steel, nickel, and copper at the temperature at 100° C., see Part II. 
