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.

    10/16 (page 8)
    There are two considerable deficiencies in this construction ; first, that the hand cannot be turned even so much as a quarter of a circle from its horizontal towards a perpendicular grasp; secondly, that there is no movement equivalent to the usual bending of the wrist, which gives so great a variety of positions to the natural hand ; indeed, it is not obvious, at first sight, how any other than an horizontal grasp can be given by this instrument, the movement of the pin M being horizontal, and paral¬ lel to itself. When, however, the hand is turned up to effect a perpen¬ dicular grasp, the action of this pin is oblique to the eye N, which then slides along it, and thus communicates its movement to the hand, full as forcibly as when it is in the horizontal position. To obviate these defects, let the wrist A, fig 3, be constructed with a hollow ball and socket movement, or other equivalent contrivance, having a range of about the eighth part of a circle ; and let this be held fast at any required point by a spring catch as before, falling into a hole in the stationary portion, which must be drilled like a sieve, to suit every position. To the inner or moveable portion the hand is fixed; and the movements of the fingers and thumb are communicated from the eye N, through a small rod B, turning on a hinge, and from thence, through a connecting-rod carrying universal joints at both ends, to a cylindrical rod, C. This rod slides freely in the tube D, and can permit one of these universal joints, E, to turn freely in a groove round it. The motion of the thumb piece F, which here, as in nature, is slower than that of the fingers, is derived from the centre pin of the joint G, passing through a slit or elongated eye in a rod hinged at the bottom, and on its prolonga. tion above, carrying an eye, forming the joint H, from whence the steel tendon, I, gives the second movement to the fingers as before. The bent finger-piece is also coupled with the end of the rod C by a short connect¬ ing piece, L. In some cases the rod B, which elongates the movement, may be dispensed with, and the universal joint E be connected directly with the joint M. It is evident, from this construction, that the grasp will be equally firm in whatever position the hand be placed, either as it respects the bending of the wrist, or its rotatory movement. In the structures before described a pressure or grasp between the thumb and fingers near their extremities is effected, and also the holding of sub¬ stances of a moderate size near the middle of the hand; and perhaps this may in most cases be as much as is required where the person employing it has only lost one hand, and can therefore do any more difficult task ■with the other ; but there are persons who have had the misfortune to lose both hands, in which case it is desirable to give this substitute all the efficient movements it is capable of. With this view, let the thumb piece.