334 Dr. F. Horton. 'Effects of Changes of Temperature [Mar. 17, 



* The Effects of Changes of Temperature on the Modulus of 

 Torsional Bigidity of Metal Wires." By Frank Horton, 

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

 Besearch Scholar of the University of Birmingham. Com- 

 municated by Professor J. J. Thomson, F.B.S. Keceived 

 March 17 —Bead April 28, 1904. 



(Abstract.) 



This paper contains an account of some experiments performed with 

 the object of ascertaining, as accurately as possible, the manner in 

 which the modulus of torsional rigidity varies with the temperature. 

 The law governing this variation has been expressed in several 

 •different forms by those who have investigated it, but all the more 

 recent experimenters have been content with finding the modulus at 

 two temperatures only and assuming a linear law to hold between 

 them. The first part of the paper contains a short account of the 

 results obtained by previous investigators, and possible sources of 

 error in the methods employed are pointed out. The rest of the 

 paper is divided into the following sections : — 



(1) Description of apparatus, etc. 



(2) Account of the experiments. 



(3) Summary of results and comparison with those of other 



observers. 



(4) Determination of the coefficients of expansion of the wires. 



The metals experimented on were copper, iron, platinum, gold, 

 silver, aluminium, tin, lead, cadmium, all chemically pure, and also 

 specimens of commercial copper and of steel pianoforte wire. The 

 wire sused were of approximately the same length and diameter, and 

 were carefully annealed before the rigidity determinations were begun. 



The method of experimenting employed was a dynamical one, the 

 torsional oscillations of the wire under test being timed by a method 

 ■of coincidences capable of great exactness. Some of the observations 

 made in the course of this work yielded what seemed to be interesting 

 information as to the internal viscosities of the wires used. This is 

 recorded in the paper and compared with similar observations by other 

 experimenters. 



The vibrator generally used was a circular disc of gunmetal, and 

 this was completely enclosed with the wire in a heating jacket, the 

 temperature of which could be varied as required. Observations of 

 the period of torsional vibration were made, in general, at five 

 temperatures, viz., at the temperature of the room, about 16° C, at 

 35° C, 55° C, 75° C, and 100° C, and also in some cases at 126° G, the 

 higher temperatures being obtained by using the vapours of various 

 liquids boiling under atmospheric pressure. 



