Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/135

Rh capable of enlarging the size of the copy. An automaton figure, exhibited in London a short time since, which drew profiles of its visitors, was regulated by a mechanism on this principle. A small aperture in the wall, opposite the seat in which the person is placed whose profile is taken, conceals a camera lucida, which is placed in an adjoining apartment: and an assistant, by moving a point, connected by a pentagraph with the hand of the automaton, over the outline of the head, causes the figure to trace a corresponding profile.

(148.) By turningThe art of turning might perhaps itself be classed among the arts of copying. A steel axis, called a mandril, having a pully attached to the middle of it, is supported at one end either by a conical point, or by a cylindrical collar, and at the other end by another collar, through which it passes. The extremity which projects beyond this last collar is formed into a screw, by which various instruments, called chucks, can be attached to it. These chucks are intended to hold the various materials to be submitted to the operation of turning, and have a great variety of forms. The mandril with the chuck is made to revolve by a strap which passes over the pully that is attached to it, and likewise over a larger wheel moved either by the foot, or by its connexion with steam or water power. All work which is executed on a mandril partakes in some measure of the irregularities in the form of that mandril; and the perfect circularity of section which ought to exist in every part of the work, can only be ensured by an equal accuracy in the mandril and its collar.

(149.) Rose Engine-turning.This elegant art de-