The Elastic Constants of Quartz Threads. 99 



the aether produces those permanent states in which there 

 is no transference of energy from one place to another is 

 difficult to explain, but it is an experimental fact which any 

 theory of the aether must necessarily explain, for it must ex- 

 plain the radiation-equality of temperature. 



If the views here put forward be correct, Sir W. Thomson's 

 objection to the kinetic theory of gases is disposed of, and 

 the many difficulties arising from the nature of the Boltz- 

 mann permanent configuration are avoided*. But the diffi- 

 culties are only avoided ; all that is done is to reduce the 

 number of properties explained by the kinetic theory, and to 

 shift the temperature difficulties to the aether, so that in some 

 shape or other they will crop up again. 



VIII. The Elastic Constants of Quartz Threads. By Richard 

 Thbelfall, Professor of Physics in the University of 

 Sydney]. 



SINCE there can be little doubt as to the great superiority 

 of quartz over silk threads for all purposes of suspension 

 where accuracy is required, I have thought it worth while to 

 obtain some detailed numerical information of their elastic 

 properties. My attention has been directed to the following 

 points suggested by the needs of instrument-making: — 



1. The determination of the strength of quartz fibres. 



2. The determination of the modulus of torsion and the 

 modulus of simple rigidity from vibration experiments. 



3. The determination of the temperature-coefficient of the 

 coefficient of torsion %. 



4. The determination of the coefficient of expansion of 

 fused quartz for the purpose of enabling a calculation of the 

 temperature-coefficient of the simple rigidity to be carried 

 out. 



5. An investigation of the amount of u Nachwirkung " ex- 

 hibited by quartz fibres with the view of finding a practical 

 limit to the rate of twist which may be safely applied. 



* I mean suck difficulties as those connected with specific heats and 

 with the proportion of the energy in the different radiations of gases ; for 

 instance, it may be urged that the molecules of sodium gas must have an 

 infinite number of degrees of freedom, since when heated sufficiently and 

 in sufficient numbers per unit volume they give out a coutiuuous "spec- 

 trum, and yet in ordinary states of vibration they give out merely, or 

 at all events chiefly, the characteristic sodium-line. 



t Communicated by the Author. 



X By " coefficient of torsion of a thread " I mean the moment of forces 

 requisite to twist the lower end of the thread through one radian, the 

 upper end being fixed. 



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