352 Note on the Tenacity of Spun Glass. 



Some observations were next made on rods about 1 millim. 

 in diameter ; tbe method of support and the loading being 

 changed. Two pieces of angle brass, each about 8 inches 

 long, were substituted for the slips of paper. Through a hole 

 drilled near the end of the angles, a piece of J" wire was 

 passed, turned up and soldered to the back. The free 

 extremities of the wires were plaited into rings, which served 

 to support the load and suspend the whole from a hook above. 



The ends of the rod were laid in the angles, leaving the 

 glass free for about 12 inches. Small pieces of red-ochre 

 cement (a compound consisting of resin, red ochre, and bees- 

 wax) were placed at intervals along the glass, and a Bunsen 

 flame applied. The cement speedily melted, and imbedded 

 the glass ; on cooling, the whole was suspended vertically. 

 A bottle was hung on the wire attached to the lower angle- 

 piece, into which a fine stream of mercury flowed from a 

 reservoir above. The apparatus was so arranged that when 

 the rod broke mercury would no longer fall into the bottle. 



The mode of measuring the diameters of the rods differed 

 from that adopted in the case of the fibres. About half an 

 inch of rod was broken away at the place of rupture, and 

 mounted in wax on a piece of looking-glass, the broken section 

 being upwards. Its diameter was then measured by means of 

 a microscope-cathetometer, and the tenacity found as in the 

 case of fibres. The following are the results of four 

 experiments : — 









Tenacity, in dynes 



•iameter, in centims. 



Weight, in 



grs. 



per sq. centim. 



0-090 



3908 





60 x 10 7 



0-082 



4443 





83 x 10 7 



0-050 



1948 





97xl0 7 



0-042 



1781 





126 xlO 7 



These observations show, in the first place, that the tenacity 

 of fine fibres is very considerably greater than that of thick 

 rods, and that the strength of rods increases as the diameter 

 diminishes. It may be interesting to point out that the 

 tenacity of glass fibres studied by us is nearly as great as that 

 assigned by Wertheim to many of the metals ; e. g., the tenacity 

 given by him for annealed steel wire 1 millim. in diameter is 

 499 x 10 7 cent.-dynes, and even in the case of drawn steel the 

 tenacity is not greater than twice that of a glass fibre, viz. 

 998 x 10 7 cent.-dynes. 



With steel pianoforte-wire the tenacity is, however, con- 

 siderably greater ; according to Sir William Thomson (Art. 



