Temperature on Modulus of Rigidity of Solid Metals. 399 



and logarithmic decrement are constant quantities, but his 

 experiments do not seem to be sufficiently accurate to 

 establish this point. 



By a series of extensive experiments on the internal 

 viscosity of wires, Tomlinson * found that in the case of iron, 

 nickel, and platinum the logarithmic decrement is less, with 

 a rise in temperature from 0° to 100° C, the percentage of 

 decrease being greatest in the case of iron. He states that 

 if w r e start with a sufficiently low temperature, the internal 

 viscosity of annealed metals is first temporarily decreased by 

 the rise of temperature and afterwards increased, and that 

 the temperature of the minimum internal viscosity is, for 

 the most annealed metals, between 0° and 100° 0. Horton f 

 also confirmed the chief results above referred to. A series 

 of very careful investigations on the viscosity of different 

 metals from liquid-air temperature to 300° was performed 

 by C. E. Guye and his co-operators J. The metals investi- 

 gated were zinc, magnesium, aluminium, silver, gold, copper, 

 platinum, palladium, nickel, iron, and steel. 'The results at 

 high temperatures agree with those of the previous investi- 

 gators, and the results at low temperatures confirm Tomlinson's 

 view just referred to in the case of gold and magnesium. 

 Quite recently, Mr. M. Ishimoto § made also the same inves- 

 tigation with the oscillating system of very short periods 

 amounting to a fraction of a second, and obtained the same 

 results. One important difference between his and the 

 foregoing results is that in the case of iron and steels a 

 sharp maximum of internal viscosity is present at about 

 70° C-, this maximum decreasing with the increase of carbon 

 content; hence the viscosity temperature curve, instead of 

 decreasing with the rise of temperature as in the former case, 

 first increases, reaches a maximum, and afterwards decreases 

 to follow the course above referred to. The following is a 

 summary of the trustworthy results so far obtained : — 



(1) The internal viscosity of different metals inei eases 

 with the rise of temperature, except in the case of some 

 metals and ferro-magnetic substances. The viscosity of the 

 latter metals first decreases with the rise of temperature, 

 reaches a minimum at about 100° C, and afterwards increases. 



* Phil. Trans, vol. clxxvii. p. 801 (1886). Proc. Hoy. Soc. vol. xl. 

 loc. cit. 



t Phil. Trans. Roy. Soc. he. cit. 



% C. E. Guye & S. Mintz, Arch, des Sci. Genive, vol. xxvi. pp. 136, 

 263 (1908); C. E. Guye & V. Freidericks, vol. xxix. pp. 49, 157, 261, 

 (1910) ; C. E. Guye & H. Schapper, vol. xxx. p. 133 (1910). 



§ Tokyo Phys. Math. Soc. vol. ix. p. 269 (1919). 



