PHILOSOPHICAL TRANSACTIONS. 



I. The Effect* of Changes of Temperature on the Modulus of Torsional 



Rigidity of Metal Wires. 



By FKANK HORTON, D.Sc., B.A., St. John's College, Cambridge; 1851 Exhibition 

 Research Scholar of the University of Birmingham. 



Communicated by Professor J. J. THOMSON, F.R.S. 

 Received March 1, Read April 28, 1904. 



TICK effect of heat upon the modulus of torsional rigidity was first studied hy 

 KUPKFER in 1848,* who investigated the changes in rigidity by observations on the 

 torsioiml vibrations of wires. This method is the one which has since found most 

 favour with experimenters, l>eing easier in manipulation and, perhaps, also capable of 

 greater accuracy than the statical method of experimenting. KUPFFKR experimented 

 on wires of iron, platinum, silver, copper, and gold, but the range of temperature 

 employed wns only that furnished by the varying temperature of the room never 

 more than 10 0. In a later papert 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. 



NAPIERSKYJ repeated KUPFKKR'S experiments with wires of iron, brass, and silver, 

 using a range of temperature of only a few degrees. 



KOHLRAUSCH and LOOMIS experimented on wires of iron, copper, and brass at 

 temperatures between 15 0. and 100 C., and came to the conclusion that for these 

 metals the rate of alteration of the rigidity modulus with the temperature was not 

 constant but increased with the temperature. Their results showed that the rigidity 

 modulus at t C. could be represented fairly accurately in the form 



n, = (1 _;_# 2 ), 

 n n being the value of the modulus at C. obtained by exterpolation. 



* ' M4m. de 1'Acad. de St. P^tereh.,' YI. ser., t. V., p. 233, 18S3. 

 t ' Mem. de 1'Acad. de St. Petereb.,' VI. ser., t VI., p. 397, 1887. 

 J Pogg. Ann.,' Krgsbd. iii., p. 361, 1853. 



' Pogg. Ann.,' 141, p. 481, or ' Amer. Journ. Sci.,' vol. 50, 1870. 

 VOL. CCIV. A 372. B 14.10.04 



