496 Mr. C. V. Boys on the Production, Properties, 



minute, the position of rest is at first moved about 1100, which 

 falls in three minutes to about 400. I have given these figures, 

 not because the effect is not perfectly well known, but to serve 

 as comparison figures to those that are to follow. They can 

 only be properly represented on a time-diagram. 



A piece of the same fibre that was used in the last experi- 

 ment was laid in a box of charcoal and heated in a furnace 

 to a dull red heat and allowed to cool slowly. This was 

 examined in the same way as the last. The effect of a 

 movement of 160,000 for one minute was now only about 60, 

 which was reduced to about 45 in three minutes. The change 

 for 480,000 lasting one minute was at first about 250, which 

 fell to about 180 in three minutes. 



Annealed spun glass then shows far less of this effect than 

 spun glass not annealed, but it is slower in recovering. It is 

 possible that if time were given, it would show as great an 

 effect as plain glass. The only mineral from which at the 

 present time I have obtained any valuable results in this 

 direction, is quartz. Here the effect of the usual minute at 

 160,000 was only 7, in the place of 370 for glass, at 320,000 

 only 17, and 640,000 only 32, which in four minutes fell to 

 22. This fibre was as usual fastened at each end by sealing- 

 wax. When this experiment was made, the thread had only 

 just been fastened. The same fibre treated previously in the 

 same way, but some days after fastening, did not even show 

 this effect ; but as this was before I had completed the 

 proper cell, the observations cannot so well be trusted. After 

 a complete turn, there was not a movement of one tenth of a 

 millim., nor had the position changed this much in 16 hours. 

 It is as yet too soon to be sure, but this seems to point to the 

 possibility of the very slight effect observed being largely due 

 to the sealing-wax. Whether this is so or not does not much 

 matter, the behaviour of the quartz thread approaches suffi- 

 ciently near to that of an ideal thread, to make it of the 

 utmost value as a torsion- thread. I hope shortly to be able to 

 bring results of carefully conducted experiments on the 

 elastic fatigue of quartz and other fibres before the notice of 

 this Society. 



A thread of annealed quartz behaves like a thread of quartz 

 not annealed. That it was affected by the process of annealing 

 is evident, because in the first place it was very rotten and 

 difficult to handle, and in the second a piece of quartz fibre, 

 which was wound up, retained its form. By this test, quartz 

 can only be partly annealed in a copper box, as any form is not 

 retained perfectly ; at a temperature above that of melting 

 copper, quartz seems to perfectly retain any form given to it. 



