1889.] 



on Quartz Fibres. 



551 



strength. I do not believe, if any experimentalist had been promised 

 by a good fairy that he might have anything he desired, that he would 

 have ventured to ask for any one thing with so many valuable 

 properties as these fibres possess. I hope, in the course of this 

 evening, to show that I am not exaggerating their merits. 



In the first place, let me say something about the degree of fine- 

 ness to which they can be drawn. There is now projected upon the 

 screen a quartz fibre one five-thousandth of an inch in diameter 

 (Fig. 6). This is one which I had in constant use in an instrument 

 and carrying about 30 grains. It has a section only one- 

 sixth of that of a single line of silk, and it is just as Fig. 6. Fig. 7. 

 strong. Not being organic, it is in no way afi'ected by 

 changes of moisture and temperature, and so it is free 

 from the vagaries of silk which give so much trouble. 

 The piece used in the instrument was about 16 inches 

 long. Had it been necessary to employ spun glass, which 

 hitherto was the finest torsion material, then, instead of 

 16 inches, I should have required a j^iece 1000 feet lono-, 

 and an instrument as high as the Eifi'el tower to put it in. 



There is no difficulty in obtaining pieces as fine as this 

 yards long if required, or in spinning it very much finer. 

 There is upon the screen a single line made by the small 

 garden sj)ider, and the size of this is perfectly evident 

 (Fig. 7). You now see a quartz fibre Jar finer than this, 

 or, rather, you see a difi"raction phenomenon, for no true 

 image is formed at all ; but even this is a conspicuous 

 object in comjDarison with the tapering ends, which it is 

 absolutely imiDossible to trace in a microscope. The next 

 two photographs, taken by Mr. Nelson, whose skill and 

 resources are so famous, represent the extreme end of a 

 tail of quartz, and though the scale is a great deal larger 

 than that used in the other photographs, the end will be 

 visible only to a few. Mr. Nelson has photographed here 

 what it is absolutely impossible to see. What the size 

 of these ends may be, I have no means of telling. Dr. 

 Eoyston Piggott has estimated some of them at less than one-millionth 

 of an inch, but whatever they are, they supply for the first time ob- 

 jects of extreme smallness, the form of which is certainly known, 

 and therefore I cannot help looking ujDon them as more satisfactory 

 tests for the microscope than diatoms and other things of the real 

 shape of which we know nothing whatever. 



iSince figures as large as a million cannot be realised properly, it 

 may be worth while to give an illustration of what is meant by a fibre 

 one-millionth of an inch in diameter. 



A piece of quartz an inch long and an inch in diameter would, if 

 drawn out to this degree of fineness, be sufficient to go all the way 

 round the world 658 times; or a grain of sand, just visible — that is, 

 one-hundredth of an inch long and one-hundredth of an inch in 



