Description of an artificial hand / By Sir George Cayley.

  • George Cayley
Date:
1845
Catalogue details

Licence: Public Domain Mark

Credit: Description of an artificial hand / By Sir George Cayley. Source: Wellcome Collection.

    12/16 (page 10)
    To avoid confusion in the figures they are drawn so as to show the movement of one finger only ; and in the hand worn by George Douseland there is but one such movement, all the cork fingers being united side by side, and fixed to one broad thin steel plate, jointed, as shown in fig. 2, and covered with continuous leather, only stitched down to mark the distinction of the fingers under it. For common use in most cases this will be sufficient; but where a more expensive apparatus can be afforded > and the appearance of having a real hand is an object, this thin steel plate can be separated into digits, though united at the base and jointed at the proper places in due proportion to each finger ; and the tendons piercing these plates may be either hinged to fixed joints, as at S, fig. 2, or worked from a horizontal extension of the joint H, fig. 3. All the required movements can be effected by catgut or other tendons attached to the joints of the fingers, as in the natural hand, and terminating in loops or eyes, on different parts of such a hinged bar as F H, fig. 3, so as to give them different ranges of tension to suit their respective purposes. This structure implies the necessity of a counteracting worm, or other spring movement, to extend the fingers and thumb again. Very light and elegant hands may be made on this plan, which would be suitable for the fair sex, and for light work. I before said, the first drawing made of the hand for George Douseland was on this plan ; but I found that he could lift the weight of five stone with the stump, and that the strength, pre¬ cision, and durability of steel joints and tendons were more suitable to his work. These have also the great advantage of giving both extension and contraction with no counteracting spring to weaken the effect. By one simple, lasting, and efficient means, both these actions are produced with perfect precision in all weathers. This instrument, in all its forms, has only been represented as working when the spring bolt L, fig. 1, secured the lower arm from turning on the hinge F ; but conceive this spring bolt occasionally drawn back, and secured from acting ; and that a spring friction plate held the joint F from turning, with less than three stone weight applied at the ring D by the stump ; the grasp of the hand could then be used only up to that extent of pressure, sufficient, say, for example, to lift a can full of liquid ; thus, if more than three stone force be applied, the friction of the joint will be overcome, the can will still be retained with the same power, but the move¬ ment of the joint will allow it to be lifted to the mouth. This is only one example of a very important principle, applicable to innumerable instances, and which greatly increases the use of the apparatus. The same principle may be carried out to a still greater extent in respect to convenient use, though not perhaps with so much power, by supplying the action of a strong spring in lieu of the friction plate. Let this spring