2 DR. F. HORTON ON THE EFFECTS OF CHANGES OF TEMI'Ki; AT! 'RE 



PISATI,* in a series of extremely thorough experiments, measured the torsional 

 rigidity of various wires over a range of temperatures from 20 C. to 300 C. He, 

 too, found that the decrease of rigidity per degree rise of temperature increased, at 

 first fairly rapidly, with the temperature, but more slowly afterwards, the rate being 

 practically constant above 190 C. The results of his experiments he expressed in a 



formula of the type 



m = n at + fit 2 yt 3 . 



ToMLlNSONt found that constant values of the rigidity modulus could only be 

 obtained after the wire under test had been very carefully annealed. He worked at 

 four temperatures between and 100 C., and his results are given in a formula 

 similar to that adopted by KOHLRAUSCH and LOOMIS. 



Exj>eriments have also been made by KATZENELSOHN,| by GRAY, BLYTH, and 

 DCJNLOP, and by SUTHERLAND,|| the latter confining his researches to the softer 

 metals, lead, zinc, tin, and magnesium, which had been neglected by former 

 experimenters. 



ScHAEFERlF worked at the ordinary temperature of the room, and at the temperature 

 of boiling liquid air. He used the statical method of experimenting by observations 

 on the torsional deflections of a wire under a constant couple. The experiments were 

 extended to a large number of elements, but observations were taken at two 

 temperatures only, and the rate of alteration of rigidity with temperature was 

 assumed to be constant between them. The main object of this research was to 

 confirm the law that if the various metals are arranged in order of ascending 

 temperature coefficients of the torsional modulus, they are also in order of increasing 

 coefficients of expansion and of diminishing melting-points. 



The rigidity of copper and steel at 186 C. has also teen investigated by 

 BENTON.** 



In view of the different results obtained by these observers, it appeared desirable 

 to repeat the determination of the rigidity modulus at different temperatures, taking 

 greater precautions to obtain a constant uniform temperature in the wire under test, 

 timing the torsional oscillations with greater accuracy, arid paying especial attention 

 to the purity and physical condition of the wires used. The experiments described in 

 the following paper were performed on wires of various pure metals and some others, 

 all of approximately the same diameter and length. The method 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 



* 'Nuovo Cimento,' ser. III., vol. 1, p. 181; vol. 2, p. 137; vol. 4, p. 152; vol. 5, pp. 34, 135, 145; 

 1877-79. 



t ' Roy. Soc. Proc.,' vol. xl., p. 343, 1886. { ' Beibl. zu den Ann.,' XII., p. 307, 1888. 



' Roy. Soc. Proc.,' vol. 67, p. 180, 1900. || ' Phil. Mag.,' [5], vol. 32, p. 31, 1891. 



f 'Ann. d. Phys.,' V., p. 220, 1901 ; IX., pp. 665, 1124, 1902, 

 ** ' Phys. Rev.,' vol. xvi., p. 17, 1903. 



