Production, Properties, and Uses of the Finest Threads. 489 



The late C. Neumann, in his pamphlet Ueber die Principien der 

 Galilei-Newtonschen Theorie (Leipzig, 1870), like Newton, postu- 

 lates an " absolute rest." He does so by assuming that there is a 

 " Korper Alpha," an ideally existing body which is absolutely at 

 rest and absolutely rigid, with respect to which the First Law of 

 Newton holds good. 



Streintz criticises this rather unintelligently, I think, for it is 

 evident in reading Neumann's essay that this is merely an awk- 

 ward and metaphorical way of stating the theory of an " Abstract 

 Dynamics." 



Note C. — The Parallelogram of Force. 



Force being defined kinetically, it is hardly necessary to demon- 

 strate this proposition. It follows as easily from the parallelogram 

 of accelerations as that does from the parallelogram of velocities, or 

 the parallelogram of velocities from the parallelogram of steps. 



This applies primarily to forces acting on a particle, but it is easy 

 to extend the theorem to " forces acting on a body," as defined in 

 the Essay. 



LYII. On the Production, Properties, and some suggested Uses 

 of the Finest Threads. By C. V. Boys, Demonstrator of 

 Physics at the Science Schools, South Kensington *. 



I HAVE lately required for a variety of reasons to have 

 fibres of glass or other material far finer than ordinary 

 spun glass ; I have therefore been compelled to devise means 

 for producing with certainty the finest possible threads. As 

 these methods may have some interest, and as some results 

 already obtained are certainly of great importance, I have 

 thought it desirable to bring this subject under the notice of 

 the Physical Society, even though at the present time any 

 account must of necessity be very incomplete. 



The subject may be naturally divided, as in the title, into 

 three parts. 



1. Production. 



The results of the natural methods of producing fibres by 

 living things, as spiders, caterpillars, and some other creatures, 

 are well knowm ; but it is useless to attempt to improve on 

 Nature in this direction by our own methods. 



Fibres are also produced naturally in volcanoes by the 

 rushing of steam or compressed gases past melted lava, which 

 is carried off and drawn out into the w 7 ell-known Peles hair. 

 The same process is employed in making wool from slag, for 



* Communicated by the Physical Society : read March 26, 1887. 

 Phil. Mag. S. 5. Yol. 23. No. 145. June 1887. 2 L 



