367 



Art. XV1II.-MISCELLANE0US INTELLIGENCE. 



I. Mechanical Science. 



1. Experiment on the tenacity of Iron Wire, by Colonel Dufour.— 

 The extreme economy and facility of construction of wire bridges* 

 are circumstances which cannot but tend to introduce them into very 

 general use: hence a knowledge of the strength of iron wire as gene- 

 rally prepared by the manufacturers, and the circumstances which. 

 have an influence over it, cannot but possess great interest. The fol- 

 lowing experiments by M. Dufour, being made with a practical 

 view, are, therefore, very valuable, and have already assisted in fur- 

 nishing data for the construction of two wire bridges across the for- 

 tification ditch of Geneva. 



The object of the experiments were to determine the absolute 

 strength of wires of different diameters ; their elongation when sus- 

 taining a given weight; the effects of a sudden concussion; ,the 

 influence ot annealing at a red heat, and the effect of a fold, or re- 

 turn, or junction of the wire, in determining rupture when in these 

 circumstances. 



Four kinds of iron wire were chosen, having the respective diame- 

 ters of 1, 2, 3, and 4 millimetres nearly. Six experiments on the 

 finest wire, of which the diameter was 0.S5, mm. (0.033 of an inch,) 

 proved that the strength was independent of the length ; that the 

 mean absolute force of such a wire was 1061bs. avoirdupois, the ex- 

 tremes being 103.7 and 120; and that when annealed, it sustained 

 oniy4rj.3lbs. Ten experiments on the second wire diameter l.g 

 mm. or 0.743 of an inch gave 432.51bs as the mean weight it could 

 sustain, the extremes being 397 and 457; from which it would appear 

 that the first wire had a seventh more of strength in proportion to its 

 diameter than the second. The second wire, when annealed, sustained 

 only 2231bs., which is to its strength when unannealed, as 100 to 194. 

 The third wire about .118 of an inch in diameter, sustained as the 

 mean of six experiments 843lbs. : when annealed its strength was to 

 that of the unannealed wire, as 100 to 195. The fourth wire, of a 

 diameter of .145 of an inch, supported l/13lbs. when unannealed, 

 and 8S9lbs. when annealed, the ratio in the two states bein" as 100 

 to 192. 



I-'rom these experiments Colonel Dufour concludes that iron wires 

 from 1 to 4 millimetres in diameter, support at least 132lbs. for each 

 square millimetre of their section. But according to known ex- 

 periments on forged bars of iron, it has been ascertained, that those 

 which are not more than 6' mm. square, do not support more than 

 from 88 to lOOlbs. per square millimetre, and those which are larger 

 only from 55 to 6'Clbs., a circumstance which sufficiently proves The 

 * See Vol. XV. pp. 13G— 373 of this Journal. 



