Declaration

another one likewise similar, and which is parallel to it, which is toward the south original: "midi". These two branches enter squarely into two perpendicular rules, parallel to the fixed leg: of which the one in the middle carries the point, and the western one must be entirely square at the end for the same reason I stated above. All of this pertains to the movement and to keeping it in proper alignment, for the rest serves as, and is the cause of, the description of the oval. At the fixed foot appear two round loops: one of which is 1 measure and 7 parts distant from the points, and the other distant from it by about 1 measure. Around each is an orb original: "orbe"; a circular disc or plate or circular body made in the fashion of a trencher original: "tranchoir"; a thick wooden plate or serving platter which is quite thick, so that a screw can enter into its thickness to tighten it against the fixed foot once it has been set by the operator. This screw is placed lower than half the thickness, so that it does not hinder a shuttle original: "nauette"; a sliding mechanical part which is in each orb, placed there so precisely that it has free movement around the fixed leg, attached to another small orb, placed above the first, which is mobile; for the first is fixed. As for the screw that appears in the shuttle, it serves no purpose, because the shuttle must be of the same piece as the slotted rule that comes into the slot where the middle perpendicular branch enters, the approach of which to the center is held by the sleeve original: "canon" which is tightened by a screw to the slotted rule. And this middle perpendicular branch has free movement over the two coming from east original: "orient" to west original: "occident", so that during movement, being pushed by the hand, it approaches and retreats from the immobile foot. This occurs because of the tilting of the orbs, for if they were upright (that is to say, parallel to the surface on which one wishes to describe the oval) one would describe a circle; but being tilted, their diameters shorten because the circumference approaches the immobile foot, which is the center. From this comes the shape of the oval, whether the rules are raised or lowered. As for the western perpendicular branch, it holds the others straight, and must be square at its bottom, needing to be tightened onto the southern branch with a screw, just as at the top toward the north original: "septentrion" it is tightened onto the northern branch. The rest of the movement is as with the others.

PROPOSITION VI.

A compass of our invention like the others, which we have for a
long time communicated to many, for describing upon a plane any
truly spiral line, without any twisting of cord, nor any other
deceptive way of doing it.

EXPLANATION OF THE SIXTH FIGURE.

The utility of this compass is no less than that of the others, since it often happens in buildings that there is a great need for this manner of line, which is usually made by means of the ordinary compass, but in several stages, it being necessary to open or close the compass while various centers upon which one works are established. However, even by that method, the line is never so natural as this compass describes it. This compass is shown in this figure complete toward the south line; the rest, which is above, are only its present or future parts. Of all these, the one closest to the entire compass is a sleeve original: "canon"; a hollow cylindrical tube or guide in which lies all the artifice of the movement of the point in a limacon original: "limaco"; a spiral or snail-shell shape. At the western end of the said sleeve is a point, which is fixed upon the surface where one wishes to describe the spiral line, so that the body of the compass turns around it, it being at the center. At the top, the sleeve has a groove or slot along its entire length, made in a dovetail original: "queüe d'hironde"; a joint shaped like a swallow's tail for stability shape, into which a rule made to match it can enter. At the western end of this rule will be the mobile point, as can be seen in the upper part, the sleeve going toward the north; and at the eastern end will be a nut original: "eſcroüe"; a threaded block, with which it is not well joined here, for what holds them together must take it from below, so that the nail does not prevent the rule from sliding easily in the slot or groove. This nut, which is joined to it, turns around the screw seen there, or is even assembled with it. This screw must be in the middle of the sleeve, having free movement on its pivot, which is placed in the round hole that appears in the complete instrument toward the west, its other end being fixed in this small wheel original: "roulette" which is near the east line. The compass being composed of all these parts, and the small wheel having free circular movement, the compass supported on it and on its point, when one moves the compass, the wheel turns by means of the teeth that are around it. And in turning, it also turns the screw which pushes the nut, which is held in alignment by the rule, which is also pushed by the same means. In such a way, bit by bit, the mobile point retreats from the center and describes the spiral; which is made in several ways, according to the screws placed inside the compass, of which two sorts are seen toward the north. As for these two screws which are on the sleeve toward the east, they serve to hold the small wheel by means of a mobile circle, which being fixed to the sleeve, allows this wheel to have its movement.