XI. On the modulus of torsional rigidity of quartz fibres and its temperature coefficient

The author recently had the honour of reading to the Society the results of some experiments in which a new method of timing by means of “coincidences”—-a method devised by Professor Poynting—was applied to an investigation of the effects of changes of temperature on the modulus of torsional rigidity of metal wires. It seemed desirable to repeat similar experiments with quartz fibres, seeing that now they are almost universally employed as suspensions in torsion instruments where accuracy is required. The modulus of torsional rigidity of quartz fibres was first investigated by C. V. Boys (‘Journal Soc. of Arts,’ vol. 37, p. 827, 1889), who found considerable variations between different specimens. The mean value of the modulus obtained by him was n = 2⋅38 x 1011 dynes per sq. centim.