418 



DR. F. HORTON ON THE MODULUS OF TOK'sIONAI. 1MC1OITY OF 



In his gravitational experiments, C. V. BOYS* found that the rigidity of quart/ 

 fibres diminished under increased longitudinal stress. The fibres used in his 

 experiments, however, were subjected to greater longitudinal stress than those used 

 in the present research, being loaded, of necessity, as nearly to the breaking-point 

 as was safe. It is probable, therefore, that the decrease of rigidity with increasing 

 tension obtained by Mr. BOYS only occurs when the fibre is loaded nearly to its 

 breaking-point. 



PART II. THE VARIATION OP THE MOIHJU-S or Uicini-rv I:I:T\VKI:\ I .V C. 



AND 100 C. 



In order to make an accurate study of the effects of changes of temperature on 

 the modulus of rigidity of the fibres, observations of the periods of torsional 

 oscillation were made at several temperatures between that of the room and 100 < . 

 These temperatures were obtained by passing the vapours of various liquids, boiling 

 under atmospheric pressure, through the jacket H of the apparatus shown in fig. -. 

 The liquids used were ether (35 C.), acetone (55 C 1 .), methylated spirit (75 C.), and 

 water (100 C.). In order that the composition of the liquid, and therefore its 

 boiling-point, might not vary, a reflux arrangement was used, the vapour being 

 driven from a large copper boiler through the heating jacket, after which it is 

 condensed by a condenser, the condensed liquid running back again into the boiler. 



The fibres used in these experiments were fixed in position by the process of 

 silvering, coppering, and soldering, the temperatures used preventing the more 

 simple methods of fixing being applied. 



In a previous research on the rigiditv of metal wires at various temperatures it 

 was found that the modulus of rigidity, in almost every case examined, gradually 

 increased as time went on. This increase was generally very small, and was greater 

 at higher temperatures than at the ordinary temperature of the laboratory. In order 

 to see if such an effect was given by quartz, observations were made at intervals, 

 while the fibres were kept continuously al a constant temperature. In the course of 



* C. V. BOYS, 'Phil. Trans.,' A, vol. 186, p. 61, 1895. 



