A treatise of artificial magnets ; in which is shewn an easy and expeditious method of making them, superior to the best natural ones, and also, a way of improving the natural ones, and of changing or converting their poles : Directions are likewise given for making the mariner's needles. In the best form, and for touching them most advantageously, &c / by J. Michell.

  • Michell, John, 1724?-1793.
Date:
1750
Catalogue details

Licence: Public Domain Mark

Credit: A treatise of artificial magnets ; in which is shewn an easy and expeditious method of making them, superior to the best natural ones, and also, a way of improving the natural ones, and of changing or converting their poles : Directions are likewise given for making the mariner's needles. In the best form, and for touching them most advantageously, &c / by J. Michell. Source: Wellcome Collection.

    12/86 (page 10)
    io A 'Trecitife of . 1 five Inches and half long, and were reckon'd to lift at firft only fifteen or fixteen Ounces, but when I faw them, they would not lift near fo much as that, probably, for want of proper precaution in keeping them. I have heard of Magnets, of the fize of thofe juft mention'd, that have lifted feven or eight and twenty Ounces: this, if true, muft have been owing probably to fome difference in the hardening the Steel, or in the Steel itfelf; or, which is moft likely, to the difference of form, or fome other circumftances in the Iron lifted; for on trying lately one of the three or four Magnets mention'd above, (which was no better than the reft, but as near as might be of the fame goodnefs with them,) I found it, juft after it was retouched, to lift an Iron Poker, weighing two and twenty Ounces, with great eafe 5 and it continued feveral days after that f From what has been here faid, I do not mean to in¬ fer the fuperiority of this Method above the Dodtor’s, but only an equality with his, (which moft probably is the fame with this;) the difference here mention’d being owing, in all likelihood, to the want of proper care in the hardening of the Steel bars, that his were made of; which is a moft material Circumftance ; for the fame bar, that, when properly hardened, may be made to lift twenty Ounces ; when greatly over or greatly underheated, will not lift above fix at the utinoft. trial