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.

  • John Michell
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.

    42/86 (page 40)
    For Mariner’s -f* Needles to carry a Card, it will be very proper, to ufe fuch bars as thofe propofed for Magnets, (or however but little fmaller in proportion to their Length,) with a hole in the middle, to let the pin, they are to reft on, pafs through, and to faften a cap in: The reafon why I would recommend fuch large bars, is becaufe the larger quantity of Steel we ufe, the more fteadily and certainly the Com* pafs will traverfe, (provided the Needle be as f Perhaps it may not be amifs to cover the Needles, made ufe of in the Sea Service, with a very thin coat of Linfeed Oil, or fome kind of Varnifh, that may keep them from rufting, which is generally reckon’d to injure all Magnetical bodies that are liable to it. Needles may be touched through fuch a coat, as well as when naked, if not according to the method for making of Magnets, at Icaji by a great number of bars applied after the method recommended for making fmall bars Magnetical. [See Page 35.] But probably the former Manner will be effectual ; for I have given a very confiderable ifrength to bars, though a card (which is many times thicker than fuch a coat,) was placed between them and the half dozen bars made ufe of to touch them. Andpojfibly fuch a coat (efpecially of Linfeed oil,J may make the Needles in time able to retain a greater degree of Magnetifm, than they otherwife would do ; for I haveobferved that painted Iron Cafements are very often remarkably Magnetical; and it is generally faid too, that they become much harder, and more brittle, for being painted ; which perhaps may be the reafon of their being fo remarkably fufceptible of Magnetifm. Mag*