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XXXIX. Note on the Tenacity of Spun Glass. 

 By E. Gibson and R. A. Gregory *. 



IT is well known that the tenacity of metallic wires increases 

 as the diameter diminishes, so that very fine wires will 

 carry much larger loads than those obtained by calculation 

 based upon the assumption that the breaking weight varies 

 as the square of the diameter. As glass can be drawn into very 

 fine fibres, we have made some observations on the tenacity 

 of this material, comparing the strength of very thin threads 

 with that of rods made from the same glass, but of much 

 greater thickness. 



The experiments were carried out in the course of our work 

 in the Physical Laboratory of the Normal School of Science 

 and Royal School of Mines. 



In dealing with a substance so brittle as glass, it is evident 

 that special care must be taken to ensure that the observation 

 is not vitiated by rupture due to a shearing stress, at or near 

 the points of support. Precautions were taken to prevent 

 this in all cases, and no experiments are quoted in this paper 

 in which rupture took place near the points of support, or of 

 attachment of the weight. 



Three different thicknesses of glass were subjected to 

 experiment : viz., fibres the diameters of which were about 

 0*002 and 0*004 centim. respectively, and rods with dia- 

 meters varying between - 05 and 0*09 centim. 



The fibres were attached at the ends of two strips of paper by 

 means of shellac varnish ; this on setting was found sufficiently 

 strong to carry more than the breaking weight, without 

 allowing the fibre to slip. A small paper basket suspended 

 from the lower strip carried the load, consisting of fine shot 

 and silica, the latter being added when the fibre was near its 

 breaking-point. 



The diameter of the thread was measured at the place of 

 rupture by means of a Compound Microscope with micrometer 

 eye-piece. From data thus obtained the tenacity was calcu- 

 lated with the following results : — 







Tenacity, in dynes 



iameter, in centims. 



B. weight in grs. 



per sq. centim. 



0*00186 



11-76 



424 xlO 7 



0*00159 



8*70 



425 x 10 7 



0*00315 



32-26 



405 x 10 7 



0*00340 



43-23 



466 x 10 7 



* Communicated by the Physical Society : read February 12, 1887. 



