. Studies in physics. ell can be seenfrom Fig. 2. The first three series of observations of Fig. 2 give the temperaturevariation of Youngs modulus with external heating. Series 11 shows thetype of curve, and the return of the modulus to the same value after aday of heating and stretching. Series 12 was taken under similar con-ditions. By yielding the same results it proves the total disappearanceof all history effects except the very gradual increase of the modulus withcontinued heating and stretching. As the observations for decreasingtemperature in the last two series were few, series 13 was
. Studies in physics. ell can be seenfrom Fig. 2. The first three series of observations of Fig. 2 give the temperaturevariation of Youngs modulus with external heating. Series 11 shows thetype of curve, and the return of the modulus to the same value after aday of heating and stretching. Series 12 was taken under similar con-ditions. By yielding the same results it proves the total disappearanceof all history effects except the very gradual increase of the modulus withcontinued heating and stretching. As the observations for decreasingtemperature in the last two series were few, series 13 was made in orderto learn whether the curve with decreasing temperature is the same as Vol. s ] ELASTICITY OF A MILD STEEL WIRE. 377 with increasing temperature. The results indicate the absence of anyhysteresis effect. In order that the various series in this and the otherfigures may be more easily compared the curve which appears was drawnto fit a composite of them all. Its shape is exactly the same in every case. Fig. 2. Change of Youngs modulus of a mild steel wire with increasing and decreasing temperature and with internal and external heating. the only difference being that it is gradually raised to correspond to thegeneral increase of the modulus as the work progressed. All of the observations so far had been made with the wire enclosed inan asbestos board heating box so that the currents used in the wire andthe heating element might be as low as possible. Walker1 has found agreat difference between the effects of internal and external heating, de-pendent in part upon the current density. He interprets these results ascaused by the magnetic effect of the current, the maximum field which hesecures having an average value of 31 gausses. When series 19 (see Table I.) was taken an attempt was made to findthis effect in case it were associated with residual magnetism. Between 1 Proc. Roy. Soc. Edin., Vol. 31, 186, 1910. 373 H. L. DODGE. [SecondISeries. the first two obser
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