On the transient magnetic state of which various substances are susceptible / [Sir W. Snow Harris].

  • Harris, W. Snow (William Snow), Sir, 1791-1867
Date:
1831
Catalogue details

Licence: Public Domain Mark

Credit: On the transient magnetic state of which various substances are susceptible / [Sir W. Snow Harris]. Source: Wellcome Collection.

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    substance, or otherwise to a ring of lead. This disc has smooth rounded edges, and is balanced on a fine central point A of hardened steel, in such way that the centre of gravity and centre of motion coincide as nearly as possible; the whole is sustained on a small agate cup, set in a short cylindrical piece of brass a, fig. 4, and screwed, when required, into the shoulder of the brass cylinder which passes through the round hole of the pump-plate as represented in fig. 6. The sliding rod n e above mentioned is in this case withdrawn for a short di- stance within the cylinder. The disc is set in motion at the rate required by means of a line wound rapidly off it, from a train of wheels; it is then covered with a screen, and with a receiver, as in fig. 6, and the exhaustion made as per- fect as possible; in which case it will continue to revolve for a considerable time. A simple or compound magnet is put into rapid rotation in a similar way, being previously mounted on a ring of lead; besides straight bars, a compound magnet was employed for this purpose, having its extremities turned up in a perpendicular direction for about an inch, as in c d, fig. 7> and occasionally a circular disc of magnetised steel, fig. 5. The former has its point of support fixed in a transverse bar of brass a b, fig. 7, which projects in a circular hole drilled through the centre of the bars.* 6. When it became necessary to measure with great precision the rapidity of rotation, the machine represented in fig. 3 & 8 was employed. It consists of a metallic disc M kept in motion by a delicate train of wheels and pinions j) j). The rapidity of the rotation being accurately measured by an index x, moving on a small circle divided into twenty parts. The weight W, fig. 3, which by its descent keeps up the rotation, falls in a tall narrow receiver r r, supported against the under surface of the pump-plate. A circular hole is drilled at s' through the plate for the silk cord to pass, from the pulley at y \ by means of this hole also, the receiver r r' is exposed to the action of the pump. The machine is wound up and set in motion by means of the brass rod n e, fig. 3, already described (4), without disturbing the state of the exhaustion; the extremity of the rod being formed into a key. The revolving disc is screened by glass or any other substance, over which * This method of obtaining a rapid rotation in an exhausted receiver, suggested itself on perusing the account of Mr. Serson’s horizontal speculum in the Royal Society’s Transactions.