Theatrum instrumentorum et machinarum Iacobi Bessoni Delphinatis ...

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THE AUTHOR’S PROPOSITION ON FIGURE IV.

A NEW COMPASS, CONTRARY TO THE PREVIOUS ONE, AS IT IS SUITABLE FOR DESCRIBING RECTILINEAR FIGURES FROM THE ORDER OF CERTAIN CONNECTED PYRAMIDS WHICH HAVE THE PRECEDING PLANE AND CURVILINEAR FIGURES AS A BASE.

Declaration of the same Fourth Figure.

Decorative drop cap 'P' featuring foliage and a human face.The parts of this Compass differ in some way from the parts of the preceding one; even if they agree with each other in certain respects. For it has an immovable Leg, and a Northern Arm rotating around it. However, if the framework of both Compasses were the same and as it is in this one, it would be far better: for they should differ between themselves only by the Pyramid. Those tables, which are in each perpendicular ruler, (within which the arms can be pushed and pulled back, to move the mobile point toward and away) serve to depress and elevate the same point; if the center and circumference are not on a flat surface. Experience will teach the diligent Reader this.

Addition.

THE small difference that exists between this and the previous Compass is described here only for the greater convenience of those progressing in Mechanics. For if they were entirely similar, they would be one and the same, because if a rectilinear Pyramid is placed in this one, it will show a rectilinear Figure: just as if a Curvilinear Pyramid is placed in that one, it will also describe the same thing that this one delineates. Our Author therefore did not lack judgment while he exhibits them to us as different in some part.

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