370 



Mr. C. Vernon Boys 



[June 8, 



but its existence is certain. In the later operations the deflections, 

 if any, due to the lid alone on the mirror alone, and to the lid alone 

 on the mirror and gold balls, are separately determined. Neither of 

 these can be detected. The actual elongation of the fibre may also 

 be observed at this stage, but this is of interest only as bearing on 

 the elastic properties of quartz fibres under longitudinal strain. 



Fig. 8. 



Before I come to the treatment of the observations, I should like 

 to refer shortly to the kind of perfection of conditions which by the 

 employment of every practicable refinement that I could devise, I 

 have succeeded in obtaining. Taking experiment 8 as an example, 

 favourable in that the conditions were good, i. e. I was not badly dis- 

 turbed by trains, wind, or earth tremors, I give the worst and the 



