THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



APRIL 1847. 



XXXVIII. 0)1 the Effects of Magnetism, Sec. upon the Dime?i- 

 sions of Iron and Steel Bars. By J. P. Joule, Esq., Se- 

 cretary of the Literary and Philosophical Society of Man- 

 chester, 



[Continued from page 87.] 



WITH a view to ascertain whether the lengthening effects 

 observed in the experiments detailed in the former 

 part of this paper were entirely independent of the diameter 

 of the bars, I made a very extensive series of experiments, in 

 which fine wires both of iron and steel, bundles of very fine 

 iron wires, chains composed of copper and iron links, &c. 

 were employed. In order to keep these flexible articles exactly 

 in the axis of the coil, a weight was placed upon one of the 

 levers, so as to exert upon them a force of tension equal to 

 about eight ounces. 



The results of the experiments in which wire of ^^^th of an 

 inch thickness was employed, accorded very well with the 

 previous experiments with thicker bars ; but on employing 

 iron wire which was only y^^jjlh of an inch thick, the phaeno- 

 mena assumed quite a different character; for on transmitting 

 the current through the coil, the length of the wire became 

 suddenly diminished instead of being increased. This phae- 

 nonienon appeared to me exceedingly anomalous, and it was 

 some time before I found out its cause. At last, thinking 

 that the wire was attracted by the coil, I varied its position 

 from the centre to either side, and increased the amount of 

 its tension. Tlie former of these operations produced no 

 sensible effect; but the increase of tension caused the shorten- 

 ing effect of the current to be considerably augmented. It 

 became manliest, therefore, that the weigiit of eight ounces, 

 acting upon very fine wire, produced the anomalies in question. 

 This was iiirllier demonstrated to be the case by diminishing 



Phil, Mag, S. 3. Vol. 30. No. 201. April 18*7. H 



