[ ±M ] 



XLIV. The Attachment of Quartz Fibres. 

 By C. V. Boys, A.R.S.M., F.B.S.* 



MEMBERS of the Physical Society may remember that 

 in 1887 f I described a method of making- fine fibres 

 of glass and other materials, bat especially of melted quartz, 

 which latter had properties of great value, rendering them 

 more suitable for experimental work of combined delicacy 

 and accuracy than those of other known materials. Experi- 

 ments made since by others as well as myself have further 

 shown that for delicate work of the highest degree of accuracy 

 they are essential. 



The method of fastening them, however, at their ends to 

 the pointed end of the torsion-pin at the top or of the 

 suspension below by shellac varnish, or better by melted 

 shellac, is apt to give rise, more especially if the fibre is 

 unskilfully laid in place so that it is twisted round the 

 point, to a slow creeping of the point of rest due to slow 

 changes in the shellac. This, except for the first few days, 

 can hardly ever be of an amount to seriously affect any ob- 

 servations ; in fact I have made many observations of the 

 effect of gravitation between small masses with fibres so 

 fastened of a great degree of accuracy, besides those with the 

 radiomicrometer, pocket electrometer, &c, without any incon- 

 venience, yet I have felt that some method of attaching them 

 which would be less likely to hold the fibre by a part in a 

 state of torsional strain or of flexure would be preferable. If 

 the part of the fibre held could certainly be in its natural 

 position and state with respect to the rest, then, even if the 

 fastening should fail to be as perfect as a true weld, any 

 resulting change of zero should be small compared to that 

 observed where the portion held is twisted or much bent. 



The process of silvering, electro-coppering, and soldering is 

 an obvious one, but it is not so easily carried out with a fair 

 degree of certainty and in a manner which is convenient of 

 application, as , might be expected. My experience of last 

 autumn has enabled me to perforin the process in a series of 

 operations, each simple enough, and, as far as I am able to 

 test it in the apparatus with which I am now measuring the 

 Newtonian constant of gravitation (which I may say is of 

 unusual delicacy), with perfect success. In this case the fibre 

 is necessarily stretched to not far from its breaking weight, 



* Communicated by the Physical Society : read February 23, 1894. 

 t Phil. Mag. June 1887. 



