I. The effects of changes of temperature on the modulus of torsional rigidity of metal wires

The effect of heat upon the modulus of torsional rigidity was first studied by Kupffer in 1848, who investigated the changes in rigidity by observations on the torsional vibrations of wires. This method is the one which has since found most favour with experimenters, being easier in manipulation and, perhaps, also capable of greater accuracy than the statical method of experimenting. Kupffer experimented on wires of iron, platinum, silver, copper, and gold, but the range of temperature employed was only that furnished by the varying temperature of the room—never more than 10°C. In a later paper an account is given of some experiments on wires of copper, steel, and brass at the temperature of the room and at that of boiling water. The coefficient of diminution of the rigidity modulus was assumed to be constant between these temperatures, and was calculated from the periods of the torsional oscillations. Napiersky repeated Kupffer’s experiments with wires of iron, brass, and silver, using a range of temperature of only a few degrees.