...figure. And it is not without reason that they are there, especially since if there were only one, the branches might shift, which these prevents. In addition to all this, there appears a Turkish arc original: "arc Turquois"; a curved brace shaped like a recurve bow used for stability and as a handle, the middle of which is joined to the center rule so that it cannot be separated, being also attached to the westernmost branch: this serves to guide the work. For once the point is positioned at the desired distance from the moving leg, with one hand placed on the fixed leg and the other on this arc, by turning, one continually pushes the center rule against the pyramid In Besson's mechanical drawing, the "pyramid" refers to a three-dimensional template or cone that dictates the path of the drawing point: so that the point moves according to the shape of the pyramid, and in turning creates a figure parallel to the said pyramid—though not exactly like those described below, for it is the other compass that creates those. Rather, this one creates figures made of straight lines, and those related to them, and many other similar ones, according to the shape of the pyramid that has been installed. This will be understood by what I have already said, which anyone with the slightest knowledge of the first elements of these sciences may test without fear.

PROPOSITION IV.

Another new compass by which one describes figures of curved

lines, which correspond to figures of straight lines, and

this according to the order of the pyramids which have figures of curved lines

for a base.

EXPLANATION OF THE FOURTH FIGURE.

This compass is joined with the other, and even if both were identical, it would matter little, for they should only differ in the pyramid, their use being entirely the same and the manner of using them being identical in every way. This one creates the figures described in the preceding portrait, insofar as the figure relates to the pyramid placed at the fixed foot of the compass. As for the rest, this one has certain particularities not found in the other, just as the other has some not common to this one. This is done so that one may use them according to convenience; for if they were both identical, it would be all the same, given that if a pyramid of straight lines is placed in this one, it will produce straight-lined figures, just as if a pyramid of curved lines is placed in the other, it will do what this one does. However, these barrels original: "canons"; hollow tubes or sleeves used to hold the drawing points which are on the perpendicular rules take the place of the holes in the other, and serve as needed if the surface is not flat—such as when the center is higher or lower than the place where the circumference must be—to raise and lower the point. The rest is similar to the other, and should be treated as such. The diligent reader will be able to recognize this if they recall what has already been said.

PROPOSITION V.

A compass not yet seen, which is universal for describing

in a single stroke an oval figure, having one of its two diameters as long

and the other as short as one wishes.

EXPLANATION OF THE FIFTH FIGURE.

The oval is a figure which, for its beauty, is often found in buildings and various designs: there are many inventions for creating it. For masons make it by fixing two points and turning a cord around them, these two points acting as a single center This describes the "string and pin" construction of an ellipse. Others make two intersecting circles passing through each other's centers, then trim them at their tops; others make them narrower, others longer; and this is not done without many strokes of the compass, which sometimes spoil the workpiece upon which the oval is being made. All of these inconveniences are prevented by means of this compass, which could be like those aforementioned if there were only one kind of oval according to a single pyramid; otherwise, infinite pyramids would be required. This excellent compass remedies that, its ingenuity and convenience yielding nothing to the others. But so that we may know them, let us understand its parts, which are as follows: namely, a fixed leg as in the others, around which the rest of the assembly turns, having the northern branch similar to that of the first compass in the third figure...

Technical