Theatrum instrumentorum et machinarum Iacobi Bessoni Delphinatis ...

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THE AUTHOR’S PROPOSITION ON FIGURE VI.

A COMPASS OF OUR INVENTION, LIKE THE OTHERS ALSO; COMMUNICATED BY US LONG AGO TO MANY, FOR DESCRIBING ANY SPIRAL LINE WHATSOEVER, ON A PLANE WITHOUT THE COILING OF A CORD, OR ANY OTHER FALLACIOUS REASON.

Declaration of the same Sixth Figure.

Decorative drop cap 'H' featuring floral and scrollwork motifs.THE entire Machine of this Compass is in the South. The remaining Northern parts are parts of it, which I wish to explain. The long and hollow round part, which it pleases me to call a Cannon from its similarity to a Bombard, is the case in which the Point is toward the West, around which the Compass rotates to describe the spiral. The next part is a screw, to whose outer part adheres a Ruler, at whose Western end is a mobile Point. The remaining other Northern parts are the inner parts of the screw, for painting a manifold Spiral line; and they are imposed in turn on the outer part of the screw. Now in the center of the Eastern small wheel, whose last edge is toothed, the square extremity of the inner part of the screw is inserted, so that with the compass composed of all its parts, the screw may be moved with the help of that wheel, and the mobile point may be gradually emitted, the ruler (which carries it) always remaining in the square slot which is in the upper part of the Cannon. Which is the proposition.

Addition.

THIS Compass, indeed, brings no less utility than the other previous ones. For it often happens that we need a Spiral line in erecting buildings. Which line, certainly, although it is accustomed to be drawn with a common compass, and not without labor; since it must be repeatedly opened and closed: yet it is scarcely ever drawn most accurately and in its own proper form, as it will be depicted by this Compass of ours. It remains therefore to notice that the slot which is above in the Case, or Cannon, is continuous; and is cut from one of its extremities to the other in that form which is commonly called a swallow's tail: as well as the ruler, which is placed into the slot itself, is both continuous and formed by similar and the same work. In addition to this, the screw must occupy the middle place in the Case, and there have free motion, resting upon its Pivot: which Pivot is indeed inserted into that round hole which is seen in the complete Figure of the whole Instrument to the West. Finally, those two screw-like Nails, which are in the Case, toward the East; have no other use than to firmly fix the Eastern toothed Wheel; and that operates with the help of that mobile orb, which is affixed to the Case, so that the wheel itself may complete its motion.

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