Elastic Constants of Quartz Threads. 101 



threads, and their limits of perfect torsional elasticity. The 

 measurements of the threads, as well as the rest of the work, 

 has been attended to by myself. 



I have found it convenient to abandon the bow-and-arrow 

 method of making threads in favour of a rather more manage- 

 able method — applicable to the production of comparatively 

 short, thick thread,-. On a board about seven feet long a brass 

 rod three quarters of an inch in diameter and six feet long 

 was fastened so as to lie parallel with the board at a distance 

 of about an inch and a half above it. On this brass rod a 

 light boxwood traveller was adjusted to slide freely, and this 

 traveller carried a rough and ready clamp. A clamp was also 

 established on the board at one end of the brass rod. A bit 

 of quarter-inch catapult elastic was fastened to the slider, and 

 fixed as to its other end to a hook screwed into the board at 

 the end furthest from the fixed clamp. This elastic was 

 brought into tension by pulling the slider up towards the 

 clamp. When in position the slider was held by a trigger, 

 actuated by foot. A combination of springs and india- 

 rubber was arranged near the hook, so as to act as a break 

 on the slider, and also to jam it in such a way that there was 

 no rebound. The slider was prevented from turning round 

 by its proximity to the board. In order to draw a thread, 

 a bar of quartz of the required thickness was clamped 

 as to its ends in the two clamps and was heated in the 

 middle. Of course, on pulling the trigger, a thread of any 

 desired thickness and about 5 feet long was produced. From 

 the middle of this thread a portion of the required length for 

 the experiment in hand was cut, and the diameters of the two 

 ends were measured. If the difference in diameter observed 

 was within the range of experimental error of measurement, 

 the thread was considered sufficiently uniform for the work in 

 hand. Some threads shot in the ordinary way were also used 

 in the breaking and vibration experiments. I venture to 

 think that in practice the catapult method of production will 

 be found useful, as it is certainly possible by means of it to 

 get a thread about four feet long at least as fine as I can 

 manipulate, though one improves in manipulation so much 

 that the experimental limit is continually moving away. It 

 must be admitted, however, that a little practice is necessary 

 in order to draw fine threads by the catapult method. The 

 strength of the fibres is such that for galvanometric purposes 

 the limit of thinness is imposed by our skill in manipulating 

 the fibres, not by their inability to carry a load. For this 

 reason, and also because the strength of fibres appears to differ 



