QUARTZ FIBERS. 



319 



Fig. C. 



Fic 7. 



line of silk, and it is just as strong. Not being or- 

 ganic, it is in no way afiected 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 10 inches long. Had it 

 been necessary to employ spun glass, which hitherto 

 was the finest torsion material, then, instead of 10 

 inches, I should have required a piece 1,000 feet long, 

 and an instrument as high as the Eiffel tower to put 

 it in. 



There is no difficulty in obtaining pieces as fine as 

 this, yards long if required, nor 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 

 I^erfectly evident (Fig. 7). You now see a quartz fiber 

 far finer than this, or, rather, you see a diffraction phe- 

 nomenon, for no true 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 otber 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 1 have no means of telling. Dr. lioyston Piggott has 

 estimated some of them at less than one-millionth of an inch, but what- 

 ever they are they supply for the first time objects of extreme smallness 

 the form of which is certainly known, and therefore I can not help look- 

 ing 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 can not be realized properly, it may 

 be worth while to give an illustration of what is meant by a fiber 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 058 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 1,000 miles of such thread. Further, the pressure inside 

 such a thread due to a surface tension equal to that of water would be 

 60 atmospheres. 



Going back to such threads as can be used in instruments, I have 

 made use of fibers one ten-thousanth of an inch in diameter, and in 

 these the torsion is 10,000 times less tliari that of spun glass. 



As these fil)ers are made finer their strength increases in proportion 



