552 Mr. a V. Boys [June 14, 



diameter — would make 1000 miles of such thread. Further, the 

 pressure inside such a thread, due to a surface tension equal to that of 

 water, would be 60 atmosj^heres. 



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

 made use of fibres one ten-thousandth of an inch in diametier, and with 

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



As these fibres are made finer, their strength increases in j)ro- 

 portion 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 pro- 

 ducing 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 j)lace 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 unstable form. It can no more exist than 

 can a pencil stand on its point. It immediately breaks up into a 

 series of spheres. This is well illustrated in that very ancient 

 experiment of shooting threads of resin electrically. When the resin 

 is hot, the liquid cj^linders which are projected in all directions 

 break up into spheres, as you see now upon the screen. As the resin 

 cools, they begin to develop tails ; and when it is cool enough, i. e. 

 sufficiently viscous, the tails thicken, and the beads become less, and 

 at last uniform threads are the result. The series of photographs 

 show this well. 



There is a far more perfect illustration, which we have only to go 

 into the garden to find. There we may see in abundance what is 

 now upon the screen — the webs of those beautiful geometrical spiders. 

 The radial threads are smooth, like the one you saw a few minutes 

 ago, but the threads that go round and round, are beaded. The 

 spider draws these webs slowly, and at the same time pours ujDon 

 them a liquid, and still further to obtain the efi'ect of launching a 

 liquid cylinder in space, he, or rather she, pulls it out like the string 

 of a bow, and lets it go with a jerk. The liquid cylinder cannot 

 exist, and the result is what you now see upon the screen (Fig. 8). 

 A more perfect illustration of the regular breaking up of a liquid 

 cylinder, it would be impossible to find. The beads are, as Plateau 

 showed they ought to be, alternately large and small, and their 

 regularity is marvellous. Sometimes two still smaller beads are 

 developed, as may be seen in the second photograph, thus completely 

 agreeing with the results of Plateau's investigations. 



I have heard it maintained that the spider goes round her web 



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