Elongation on the Section of Hard-drawn Wires, 357 



is difficult to avoid fracture. We hope, however, to make a 

 more systematic investigation, and to get over these difficulties 

 by improved apparatus and methods of experiment. 



Confining our attention to the brass and German-silver 

 wires, the results indicate that if the stretch does not amount 

 to more than from 20 to -^ of 1 per cent, the diameter 

 increases. The elastic effect previous to the point where 

 stretching is about to begin is for those wires in accordance 

 with other well-known results of experiments on this subject, 

 in so far as the diameter diminishes with increase of length ; 

 but we have not yet got a means of measuring with such 

 accuracy as to give quantitative results as to the ratio of con- 

 traction to extension. The change from contraction to expan- 

 sion seems to take place very near to the limit of elasticity, if 

 not after that limit has been reached. A short distance 

 beyond this limit contraction again sets in ; and if the exten- 

 sion be as much as half of 1 per cent., the diminution of 

 density, although noticeable, is not sufficient to produce 

 increase in diameter. 



The method of experiment which was used for the observa- 

 tions on which we base some of the above remarks on the 

 effect of elastic stretch, was to pass the wire along 

 the axis of a glass tube about 5 millimetres in dia- 

 meter, which was hung on the wire in the manner 

 indicated in the sketch by means of a rubber stopper s. 

 The tube was then filled with water, and the position 

 of the surface of the water read on a scale fixed on 

 the back of the tube. The wire was then stretched 

 and the fall or rise of the water observed. A dimi- 

 nution of volume was observed until the wire reached 

 about the elastic limit, at which point the water rose, 

 slightly indicating a swelling of the wire. We have 

 made several attempts to increase the sensibility of 

 the above arrangement by means of index-tubes 

 fused into the side of the main tube, aided by narrow 

 contractions in the tube, itself filled with mercury, 

 from which the wire was protected at that point by 

 a thin coating of shellac varnish. As yet, however, 

 we have not been perfectly successful. The unstable 

 condition of the mercury in the narrow contraction W\ 

 of the tube renders this method unsatisfactory. 

 Should mercury-tubes prove superior, however, in 

 experiments with iron and steel, we will platinize the 

 other metals and use mercury. 



The following are a few of the results obtained by the 

 measurement of density before and after stretching, the 



Phil. Mag. S. 5. Vol.' 29. No. 179. April 1890. 2 E 







