Elastic Constants of Quartz Threads. 



117 



The mean value of Young's modulus found was 



Quartz fibres, whether thick or thin (i. e. weak or strong), 

 all increase in tenacity as they are dissolved by hydrofluoric 

 acid ; so that no matter whether a thick or thin fibre was used 

 at first, the diameter is found to be the same at the moment 

 that it is broken by the pull of a given weight suspended 

 from it, showing that it is neither a vitreous skin nor an effect 

 of annealing that gives the fine fibres so great a tenacity. 

 Quartz fibres dissolve very slowly in hydrofluoric acid in 

 comparison with spun glass. 



The experiments on the elasticity of quartz threads were 

 made with a machine, for a description of which I must refer 

 those interested to the Journal of the Society of Arts. 



6 x 10 11 

 the modulus of torsion . . 3 # 74 x 10 11 

 '„ „ the rigidity 2*38 x 10 u 



I also gave (p. 17 of the reprint) full directions for mounting 

 quartz fibres, which will possibly be worth referring to by 

 those who may wish to acquire the easy act of handling these 

 delicate filaments. 



I should like to take this opportunity of publishing measures 

 of the refractive power of fused quartz recently made by Mr. 

 W. Watson in the Physical Laboratory at South Kensington, 

 using a prism of this material that had been ground and 

 polished by my friend Mr. Cunynghame. This piece of 

 quartz I had annealed by allowing it to cool slowly in the 

 centre of a furnace of pure broken quartz heated by a large 

 oxy hydrogen-flame. Mr. Watson also measured the refractive 

 index of a piece of crystalline quartz at the same time for the 

 purpose of comparison. 



1 



Fused Quartz prism. Angle 57° 7' 40". 



Crystalline Quartz 



prism. 



Angle 60° 12' 50". 



(Mean of two lines.) 



Metal used to 

 give line. 



Wave-length. 



Refractive 

 index. 



Refractive index. 



Lithium 



Sodium 



6705 



5892 



1-4560 

 1-4587 

 1-4608 

 1-4647 

 14681 



1-5415 

 1-5443 

 1-5469 

 1-5507 

 1-5556 



Thallium 



Strontium 



Rubidium 



5349 

 4607 

 4209 



