Abstract
DR. JOULE long since discovered that when a bar of iron was magnetised by an electric current, an elongation of the bar took place. In subsequent experiments, published in 1847, Joule found that the elongation amounted to about 1-200,000th of the length of the bar for the maximum magnetisation, and that the total elongation was nearly proportional to the square of the actual magnetisation. By placing the bar in a vessel of water stopped with a capillary tube, it was found that the volume of the iron did not augment, and hence Joule concluded that the sectional area diminished in proportion to the elongation. Under longitudinal tension, magnetisation caused a shortening of the rod when the tension exceeded 600 lbs. for a rod a quarter of an inch square. Soft steel behaved like iron; but hard steel, under all circumstances, Joule found to shorten slightly when the magnetising current passed
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On the Alterations in the Dimensions of the Magnetic Metals by the Act of Magnetisation . Nature 26, 585–586 (1882). https://doi.org/10.1038/026585b0
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DOI: https://doi.org/10.1038/026585b0