344 Stress and Strain and the Properties of Matter. [May 6, 



Table II. 



Metal. 



Formula for tlie logarithmic decre- 

 ment due to internal friction be- 

 tween 0° C. and 100° C. 



X, and X represent the logarithmic 

 decrements at *° C. and 0° C. re- 

 spectively. 



Percentage decrease 

 or increase of the 

 logarithmic decre- 

 ment when the tem- 

 perature is raised 

 from0°C.to 100° C. 

 — signifies decrease 

 + „ increase. 



Silver 



Platinum 



Platinum-silver 

 Aluminium. . . . 



X, = X (l _ -01244* + ' 0003016* 2 ) 

 X f = X (l - • 01235 * + • 0001040* 2 ) 

 X ; = X (1 + • 01410* + • 0001005 f 2 ) 

 X, = X (l -0 -00806* + -0006644*-) 

 X, = X (l + • 01413* + • 0007122* 2 ) 

 X f = X (1 + -00057* -0 -0000205* 2 ) 

 X, = X (1 -0 -01599* + • 0000814* 2 ) 

 X, = X (l-0 -01801* + -0006345* 2 ) 



+ 177-2 



- 19-5 

 + 141-6 

 + 583-8 

 + 853-5 



- 14-8 



- 78-4 

 + 454 -4 



days to two months. This treatment consisted in repeatedly heating 

 the wire to 100° C, and then cooling it again until the torsional 

 elasticity and the internal friction both became constant at all the 

 temperatures at which the wires were tested, and produced the 

 following permanent effects : — 



(a.) Very appreciable increase of the torsional elasticity in the 

 case of some metals and appreciable increase of the torsional elasticity 

 in all cases. 



(b.) Large diminution of the internal molecular friction, the effect 

 on the friction being considerably greater than the effect on the 

 elasticity. 



(c.) Very appreciable increase of the limiting amplitude beyond 

 which the logarithmic decrement ceases to be independent of the 

 amplitude. 



From a consideration of Tables I and II it may be gathered 

 that : — 



(cZ.) The torsional elasticity of all metals is temporarily decreased 

 by rise of temperature between the limits of 0° C. and 100° C, the 

 amount of decrease per degree rise of temperature increasing with the 

 temperature. To this may be added that the percentage decrease of 

 torsional elasticity produced by a given rise of temperature is for most 

 metals about twenty times the corresponding percentage increase of 

 length. 



(e.) If we start with a sufficiently low temperature the internal 

 friction of all annealed metals is first temporarily decreased by rise of 

 temperature and afterwards increased. The temperature of minimum 

 internal friction is for most annealed metals between 0° C. and 



