July II, 1889] 



NATURE 



249 



have to do is to liberate the string of the bow by pulling the 

 trigger with one foot, and then if all is well a fibre will have 

 been drawn by the arrow, the existence of which can be 

 made evident by fastening to it a piece of stamp-paper. 



In this way threads can be produced of great length, of 

 almost any degree of fineness, of extraordinary uniformity, 

 and of enormous strength. I do not believe, if any ex- 

 perimentalist 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 fineness 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 loaded with about 30 grains. 

 It has a section only one-sixth of that of a single line of 



Fig. 5. 



silk, and it is just as strong. Not being organic, it is in 

 no way afifected 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 piece 

 icoo feet long, and an instrument as high as the Eifiel 

 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'spider, and the size of this is perfectly evident (Fig. 7). 

 You now see a quartz fibre far finer than this, or, rather, you 

 see a diffraction phenomenon, fornotrue image is formed at 

 all ; but even this is a conspicuous object in comparison 

 with the tapering ends, which it is absolutely impossible 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 im- 

 possible to see. What the size of these ends may be, I 

 have no means of telling. Dr. Royston Piggott has esti- 

 mated some of them at less than one-millionth of an inch, 

 but whatever they are they supply for the first time objects 

 of extreme smallness the form of which is certainly known, 

 and therefore I cannot help looking upon them as more 

 satisfactory tests for the microscope than diatoms and 

 other things of the real shape of which we know nothing 

 whatever. 



Since figures as large as a million cannot be realized 

 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 diameter — would make 

 1000 miles of such thread. Further, the pressure inside 



11 



Fig. 6. 



Fig. 7. 



such a thread due to a surface tension equal to that of 

 water would be 60 atmospheres. 



Going back to such threads as canbe used in instruments, 

 I have made use of fibres one ten-thousandth of an inch 

 in diameter, and in these the torsion is 10,000 tim.es less 

 than that of spun glass. 



As these fibres are made finer their strength increases in 

 proportion to their size, and surpasses that of ordinary bar 

 steel, reaching, to use the language of engineers, as high 

 a figure as 80 tons to the inch. Fibres of ordinary size 

 have a strength of 50 tons to the inch. 



While it is evident that these fibres give us the means 

 of producing an exceedingly small torsion, and one that 

 is not affected by weather, it is not yet evident that they 

 may not show the same fatigue that makes spun glass 

 useless. I have therefore a duplicate apparatus with a 

 quartz fibre, and you will see that the spot of light comes 

 back to its true place on the screen after the mirror has 

 been twisted round twice. 



I shall now for a moment draw your attention to that 

 peculiar property of melted quartz that makes threads 

 such as I have been describing a possibility. A liquid 

 cylinder, as Plateau has so beautifully shown, is an un- 



