102 Prof. Richard Threlfall on the 



according to the amount of annealing they have received, 



and possibly also according to their thickness, per se, the 



measurement of breaking-strength was only comparatively 

 rough. 



Breaking-Strength of Fibres. 



Two methods were used. In one a small paper bucket was 

 fastened to a fibre by a silk thread, so as to avoid giving the 

 fibre any lateral strain. The load was applied by allowing 

 mercury spray from a fine pipette to gradually pass into the 

 bucket. The weight of the bucket of mercury was ascertained 

 as soon as the fibre broke. The second method was certainly 

 more convenient, and considerably more accurate, in that it 

 did not lead to vibration being set up in the thread. In it use 

 was made of a brass spring. A microscope stand was taken, 

 and the top of a spiral hard brass spring (made of wire '044 

 centim. diameter of some thirty-one convolutions, and having 

 a diameter of *95 centim.) was fastened to the structure which 

 normally carries the sliding-tube of the microscope. The 

 upper straight part of the spring had a point of reference 

 moving over a scale engraved on looking-glass, and to the 

 bottom of the spring the top of the thread was attached by 

 hard paraffin or shellac; the bottom of the thread was fastened 

 to , the base of the apparatus, and the rack and pinion was 

 worked till the spring was just on the point of beginning to 

 be stretched. The position of the point of reference on the 

 scale was then noted, and the rack screwed slowly and steadily 

 up till the thread broke. Watch was of course kept on the 

 point of reference, and its position when the thread broke was 

 noted. By afterwards loading the spring with known weights 

 — the mercury-bucket for instance — the tension exerted by 

 the spring could be estimated. It elongated 1*45 centim. 

 with 5 grammes weight, and 2'9 centim. with 10 grammes 

 weight. The method is open to the objection that a twisting 

 couple, due to the uncoiling of the spring, as well as a pull, 

 acts on the fibre. This was eliminated as far as possible by 

 making the convolutions close together, and the twist was not 

 in any case more than a few degrees per inch of length of 

 fibre. The length of the thread varied in different experi- 

 ments, as will be seen from the table. The fracture was some- 

 times curious, and in one instance, owing presumably to 

 splitting, the lower end of the thread was found to present 

 a perfect point at the position of fracture. The following- 

 abstract of results will be sufficient: — 



