116 Prof. C. V. Boys on the 



The resistance to compression can now be found by the 

 usual formula — assuming that the threads are isotropic, 



dn — 3/jl' 



This gives K = 1-435 xlO 11 . 



The results of the investigation can now be summed up as 

 follows (the numbers refer to the C.G.S. system) : — 



Simple rigidity of quartz fibres at 22° C, 



n = 2-8815xlO u . 

 Young's modulus of quartz at 23° C, 



^=51785 xlO 11 . 

 Bulk modulus, 



K=l-435xlO u . 



Temperature-coefficient of stiffness 22°-98° C, 

 e = -000133. 



Approximate coefficient of linear expansion of quartz 80° C- 

 36° 0., 



«' =-0000017. 



Corresponding approximate temperature-coefficient of n 

 = +0-00013, 



Limit of allowable twist in round numbers, one 

 third turn per centimetre in a fibre -Ol centimetre 

 diameter. 



Sydney, March 26, 1890. 



Note on Prof. Threlfall's Paper "On the Elastic Constants of 

 Quartz Threads:' By C. V. Boys, F.R.S. 



As Prof. Threlfall has asked me to look over the proofs of 

 his paper on the Elastic Constants of Quartz Threads, I am 

 taking the liberty of sending, by way of comparison, the 

 results obtained at South Kensington, which were published 

 for the first time at one of the Cantor lectures delivered at the 

 Society of Arts in the spring of 1889. It will be seen that 

 though we have not investigated the subject quite so systema- 

 tically as Prof. Threlfall, our results and his agree within the 

 limits of experimental error. 



tv I cau fin inches .... '00069 -00019 



Diameter or fibre < . .. ■ AA1 „, AAA , 



( in centimetres . . '00175 -00048 



m -i / tons to the square inch . . 51'7 74*5 



±enacity j ^^ ^ ^ ^^ centim> g x 1Q9 n . 5 x 1Q9 



