s 
364 PROCEEDINGS OF SECTION A. 
ment making), and practically identical with the 
temperature co-efficient of the “modulus of torsion.” 
. The co-efficient of expansion of fused quartz—a datum 
requisite for the calculation of (3) from (4). 
. The Young’s modulus of quartz fibres. 
Calculation of the bulk resilience from the foregoing. 
. General investigation as to the limiting intensity of 
torsional strain which may be given to a quartz fibre 
without making it exhibit torsional fatigue or 
nachwirkung. 
(1.) The breaking strength turned out to verify Boys’ estimate 
of from 50 to 70 tons per square inch. A new method, involving 
the use of a spiral spring of brass wire was used for producing 
the stresses. 
(2.) The simple rigidity was calculated from vibration experi- 
ments made in an exhausted vibration box. The mean value of 
several experiments on different fibres was— 
W = 2°8815 x 10" C.G. S. at 22°C. 
(3.) The temperature co-efficient of the simple rigidity is 
calculated from the next series of experiments by means of a 
value for the co-efficient of expansion of quartz, which was the 
average of a large number of unsatisfactory experiments— 
it is +0 00013 per degree cent. 
(4.) Determined from experiments on three fibres which were 
heated and vibrated in a special and ratber elaborate piece of 
apparatus. In order to overcome an experimental difficulty, a 
method of soldering quartz to brass was devised, depending on 
the coating of the quartz with platinum. This datum gives the 
co-efficient of increase of torsional rigidity of any cylindrical fibre, 
and is the number which must determine the amount of tempera- 
ture correction to be used in any instrument in which quartz 
fibres are employed. The co-efficient e=-00013307 between 
22° and 98°C. 
(5.) The co-efficient of expansion of fused quartz was got from 
an experiment on about 14 grammes of fused quartz, by Matheson’s 
method of weighing in water at different temperatures. The 
results were such as to show that the expansion of sticks of fused 
quartz is very irregular. The most probable value over the range 
30°—100° is at =-0000017 (co-efficient of linear expansion). 
(6.) Young’s modulus was got by bending a thread of quartz, 
supported at each end on a knife edge, by a platinum wire rider. 
Several experiments agreeing very well gave M = 5.178 x 10” 
C.G.S. Which in combination with the result (2) gave. 
(7.) Bulk modulus or resilience K = 1:435 x 10" C.G.S. 
(8.) The tests as to torsional fatigue and nachwirkung were 
made in the usual way, and showed that no fatigue is to be 
apprehended in any experimental use to which quartz fibres are 
likely to be put. As to nachwirkung, the usual symptoms were 
Or 
[ool Mor) 
