On the Effects of Chanr/cs of T<'nt/>rir'ture on Metal JVires. 187 

 Coefficients of Diminution of Young's Modulus with Temperature. 



lytic) 0-000436 as against 0-000414 for "a specimen of copper," and 

 for soft iron 0*000166 as against 0-000157, so that there is fair agree 

 ment. 



The difference between the coefficients for commercial copper (which 

 was ordinary copper wire of the kind used by bell-hangers) and electro- 

 lytic copper is very great, but it is not more striking than the difference 

 between the electric conductivities of the two materials. 



It was thought desirable to make a series of determinations for soft 

 iron with the view of finding whether any progressive change due to 

 alternate and repeated heating and cooling disclosed itself as in Mr. 

 Shakespear's experiments. Nothing of the nature of change of sign 

 (see Mr. Shakespear's paper) was observed, though there was some in- 

 dication of a diminution of the coefficient. 



Experiments on the Rigidity Modulus, and Observations on the Internal 

 Viscosity of the Wires. 



Experiments were made on each wire, as has been stated above, to 

 determine the change of rigidity produced by the alteration of tem- 

 perature. These experiments were made by the torsional oscillation 

 method. Cylindrical vibrators were attached to the wires such that 

 the moment of inertia of the vibrating system was practically that of 

 the cylinder only ; and observations were made for each wire with two 

 separate vibrators of different weights, except in the cases of German 

 silver and steel, for which one vibrator only was used, and electrolytic 

 copper, for which four vibrators were used. 



The length of wire used was, with the vibrator attached, about 

 505 cm. in each case. The lengths and radii at the different tempera- 

 tures were calculated from the expansions as in the Young's modulus 

 experiments. The results of the experiments are given in the following 

 table : 



