Elastic Constants of Quartz Threads. 109 



Fibred. 



I = -36407. I- 16-976. >>=-002455. 

 T from five sets of 200 vibrations each. T = 3*7148. Tem- 

 perature 24° C. 



n = 3-0987 x 10 u . 



Discarding the value got for fibre 0, for the reason given, 

 the mean value for n at the temperature of 21° to 23°*5 G. is 



n=2-8815xlO n . 



Determination of Change produced in Modulus of Torsion 

 of Quartz Fibre by Heating. 



For this experiment it was not essential that the fibre 

 should be uniform. On the other hand, the vibrator required 

 to be heavy, or rather to have a large moment of inertia, so 

 that the energy possessed by it might be sufficient to carry it 

 through a good many vibrations. The cylinders were used in 

 these experiments. One was about '8 centim. in diameter and 

 weighed about 10 grammes. The other, similar in figure, 

 weighed about 25 grammes. * It was very necessary to devise 

 a means of fastening the fibre rigidly to the suspender and to 

 the vibrator, as, of course, at the upper temperature all 

 ordinary cements become unreliable. 



I finally hit on a method which I have since found useful 

 for some purposes in the case of glass. It was suggested by 

 Professor Kundt's method of preparing metal surfaces on 

 glass. Two thin needles of quartz, each about two centim. 

 long and one millim. in diameter, were coated each on one 

 end for a distance of, say, five millim. with metallic platinum. 

 This was done by dipping the end in strong solution of 

 platinum tetrachloride, and subsequently reducing the same 

 by heating in a Bunsen flame. The heating requires to be 

 done with judgment. If the oxy hydrogen jet is used the 

 platinum gathers into drops ; if, on the other hand, the 

 temperature be below a good red heat, the platinum does not 

 reduce or stick properly. Having got the ends of the quartz 

 needles platinized, they are dipped in solution of chloride 

 of zinc and then tinned in the ordinary way with a small 

 iron. A hole is drilled in the vibrator and another in the 

 suspender, and these holes are tinned. It is then easy to 

 solder each needle into its respective hole, just as if it were a 

 wire. Unless care be taken not to cool the soldered parts 

 too rapidly, the quartz will be found to be rotten near the 



