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 pulley that is attached to it, and likewise over a larger wheel moved either by the foot, or by its connection 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 depends in a great measure on copying.  Circular plates of metal called rosettes, having various indentations on the surfaces and edges, are fixed on the mandril, which admits of a movement either end-wise or laterally:  a fixed obstacle called the ‘touch’, against which the rosettes are pressed by a spring, obliges the mandril to follow their indentations, and thus causes the cutting tool to trace out the same pattern on the work.  The distance of the cutting tool from the centre being usually less than the radius of the rosette, causes the copy to be much diminished.

150.  Copying dies.  A lathe has been long known in France, and recently been used at the English mint for copying dies.  A blunt point is carried by a very slow spiral movement successively over every part of the die to be copied, and is pressed by a weight into all the cavities; while a cutting point connected with it by the machine traverses the face of a piece of soft steel, in which it cuts the device of the original die on the same or on a diminished scale.  The degree of excellence of the copy increases in proportion as it is smaller than the original.  The die of a crown-piece will furnish by copy a very tolerable die for a sixpence.  But the chief use to be expected from this lathe is to prepare all the coarser parts, and leave only the finer and more expressive lines for the skill and genius of the artist.

151.  Shoe-last making engine.  An instrument not very unlike in principle was proposed for the purpose of making shoe lasts.  A pattern last of a shoe for the right foot was placed in one part of the apparatus, and when the machine was moved, two pieces of wood, placed in another part which had been previously adjusted by screws, were cut into lasts greater or less than the original, as was desired; and although the pattern was for the right foot, one of the lasts was for the left, an effect which was produced by merely interposing a wheel which reversed the motion between the two pieces of wood to be cut into lasts.