Theatre of Instruments and Machines

for painting a spiral line in many ways, and they are imposed in turn on the outer part of the screw. Now, in the center of the eastern small wheel, whose last rim is toothed, the square extremity of the inner part of the screw is fixed, so that with the compass composed of all its parts, the screw is moved by the help of that small wheel, and the movable cusp is gradually emitted, the rule (which carries it) always remaining in the square slit which is in the upper part of the cannon, which is the proposition.

PROP. VII.

A new and geometric lathe for reducing any cylinder and cone into an oval shape with its [ornaments, from any material that can be turned].

The knowledge of this lathe will perhaps delight you if you understand its parts. The base is as in common ones, but from the supports, two immovable heads (so to speak) protrude; for others are moved, which one can see from the figure. In the upper part of these is a slit, so that the table can be freely depressed and raised in it by the motion of the orbs lying between the heads. For there are two orbs, one eastern, the other western, which are disposed as in the compass for describing an oval; to these orbs the aforementioned movable table sits, in whose holes an iron instrument is placed, whence it happens that by the motion of the orbs it is depressed or elevated, so that the cylinder is turned in the manner of an oval. The rest are clear from the appearance of the figure.

PROP. VIII.

Another type of lathe, arising from the previous one, for turning, excavating, and adorning in the shape of an egg, dishes [and small pitchers, from any material capable of enduring iron].

This lathe, as the proposition suggests, depends on the preceding one, and with that understood, there is no obscurity in this figure. For in it is seen the aforementioned small orb, upon which the oval description depends. For this small orb forces the iron of the operator, which is seen placed in the perpendicular slits of the heads, from East to West. The rest can be gathered from what has already been said and from the figure.

PROP. IX.

A third type of lathe, not lacking in subtlety, for carving step-by-step the inner part of a screw of any [form on the circumference of any round and solid figure, or even an oval and conoid].

With the compass adapted for describing a spiral line understood, all things of this lathe will be easy. But so that they are better understood, I am pleased to explain them piece by piece.

Two supports protrude toward the North by 2 measures, in whose western projection one part of the work is sustained. Also, between these are three movable heads, of which the western one is larger, but the others equal, in which the screw moves freely, by whose outer part being fixed, the inner one (at the time of motion) is moved toward and removed, so that its western part, adhering to the iron instrument, is led and drawn back. Above, to the North, at 1 measure and 19 parts counted from the base of the lathe, a rod revolves, around whose middle and extremities cords are wrapped; the middle one of these is pulled by the hand of the craftsmen on one side, while the other is pulled by the weight of a mass, just as others are, in the similar part of which is a weight, and at the other extremity they are attached to the revolving rod. The eastern cord, however, is gathered orbicularly around the extremity of the inner part of the screw, whence the screw is moved. The western one, however, surrounds the last part of the work. Now remain those things which concern the motion of the iron instrument. For the painter erred in the instrument itself: for it must be moved up and down in the beam, which is led from the last part of the inner screw. The parts, however, which effect its motion are: a beam, parallel to the ground, 2 measures and 18 parts long, which receives motion from the foot of a man, at whose eastern and western ends are fixed two beams similar to it, but not so long. Also, two protruding small arms appear, in which are pulleys around which cords are emitted from those beams, from one part of which the weights hang. The figure will teach this.

PROP. X.

Finally, another type of lathe not yet seen, for polishing and cutting marble, or stone of any species, even [the harder sort, into pieces for the ornaments of sumptuous buildings].