WIRE-ROPE 1153 



what may bo termed the domestic applications of wire. Wire fences, bell-pulls, and, in 

 the form of gauze, to ventilators, are only a few of these. Another most interesting 

 employment of wire, even in a strictly scientific sense, is for the strings of pianofortes. 

 Steel wire is now solely used for this purpose. Professor W. Polo, at the request of 

 tho Messrs. Broadwood, the pianoforte-makers, some time ago made a number of 

 experiments on this kind of wire ; of which he gave a short account at tho Birmingham 

 Institution of Mechanical Engineers. Some of the steel wire he tested, which was 

 made in Germany, bore as much as 110 and 120 tons to the square inch, or about 

 double tho breaking strength of good steel. Suspension bridges, a few years ago, used 

 to be made very extensively of wire. The two most celebrated erections of this kind 

 are those of Niagara and Freiberg; the wire of the first was made in Manchester, 

 and broke at 40 tons to the square inch, while that of Freiberg was made in Switzer- 

 land, and stood 50 tons to the square inch. Tho carding of wool and cotton is also 

 effected by means of wire. Brushes of all kinds are now made of steel and iron in this 

 form, even hair-brushes. It is more than probable that wire would be much more used 

 for constructive purposes if some good and generally applicable means for preventing 

 the corrosion of iron and steel could be brought forward. In fact, that is, for all 

 applications of iron, almost tho problem of the day. It has been noticed by careful 

 observers that, though Swedish charcoal iron-wire has about the same ultimate 

 breaking tensile strength as other wire, it is nevertheless much more economical 

 than common wire for rope and other purposes in which elasticity and supple- 

 ness are required another proof that breaking strength alone is a very unreliable 

 quality. 



Tho ultimate strength of wire generally, and especially that of iron and steel 

 wire, almost always decreases as the diameter increases as is also the case with 

 forged and rolled bars, in which the metals are united in greater bulk. Some 

 very small kinds of charcoal wire only break with loads of about 100 tons to the 

 square inch ; while the average strength of wire may bo taken as double that 

 of rolled bar. Rolled bars, of various qualities, possess breaking strengths ranging 

 from 20 to 40 tons to the square inch, and iron wire will, on an average, be 

 also found to vary from 40 to oven 80 tons to the square inch. The most extensive 

 series of experiments on wires has boon due to M. Leblanc, who built a rather con- 

 siderable bridge of wire at Koche-Bernard, in France. Amongst other important 

 inquiries, ho also investigated the question whether wires of a great length did not 

 give less resistance than shorter lengths on account of the probable greater number 

 of flaws. Ho thus took from twelve sets of different wire twelve pieces two meters 

 long and twelve pieces twenty-six meters long, and submitted them to tensile loads. 

 The wire was rather more than one-eighth of an inch in diameter. The resistance 

 of the short pieces was found to be almost the same as that of the long lengths. By 

 means of some experiments extending over a lengthened period, M. Leblanc also 

 found that a wire can support during three months a tension at least equal to nine- 

 tenths of that which would break it without diminishing its ultimate breaking strength, 

 though undergoing elongations of 0-00596 of its original length. General Morin 

 also carried out, some years ago, a number of experiments on long lengths of 

 wire, in order to determine the important question whether wires take a permanent 

 set with the smallest loads : a fact maintained by Mr. Hodgkinson, and which would 

 appear to militate against the doctrine of the elastic limit. The trials were conducted 

 with very great nicety, and their results seem to show that tho permanent sets ob- 

 served by Mr. Hodgkinson were due to the bends taken by the wire when coiled, and 

 which afterwards get stretched out under the loads, as also partly to variations of 

 temperature. In general it may be observed that wire, as compared with bar iron, 

 seems to be better for undergoing impulsive forces, as it is perfectly elastic under 

 loads which, cross-section for cross-section, would break rolled or forged iron. Both 

 rolled iron and wire seem to be able to support for a length of time static loads of an 

 amount very near that which would produce rupture. Tho elongations are also in 

 proportion to tho loads, but this proportionality seems to cease sooner with wire 

 than with wrought iron. The irregularity of the elongations begins with wrought 

 iron with loads of about half the breaking loads, and with wire at about one- 

 third or one-fourth of the load that would cause rupture. Annealing, or cooling 

 clown slowly from a red heat, has the same effect on wire' as on wrought iron ; that 

 is to say, tho ductility, and the softness, of both is increased, but their elasticity, 

 and also breaking strength, are considerably diminished. But few experiments 

 have yet been published on the strength and other mechanical qualities of steel wire. 

 It may, however, be taken to have, on an average, twice the ultimate strength of iron 

 wire, and a proportionately greater elasticity, comparing diameter with diameter. 

 These qualities allow steel wire-ropo to be mado little nioro than half the weight of 

 iron wire-rope, with the same ultimate breaking strength. The additional elasticity 



VOL. III. 4 E 



