an instrument designed for drawing figures in what proportion you please, without any skill in the art.

It consists of four bras or wooden rulers, two of them from 15 to 18 inches long, and the other two half that length. At the ends and middle of the long rulers, as also at the ends of the shorter, are holes, upon the exact fixing of which the perfection of the instrument chiefly depends. Those in the middle of the long rulers are to be at the same distance from those at the ends of the long ones, and those of the short ones so as to form a parallelogram. It is fitted together by a large pillar a, having at one end a screw and nut, whereby the long rulers are joined, and at the other a little knot for the instrument to slide on: b is Pentagraph a rivet with a screw and nut, wherewith each short ruler is fastened to the middle of each long one; c is Pentapolis, a pillar, one end whereof being hollowed into a screw, Plate has a nut fitted to it: at the other end is a worm to CCXXXIV screw into the table when the instrument is to be used; it joins the ends of the two short rulers: d is a pen or pencil screwed into a little pillar: e is a bras point moderately blunt, screwed likewise into a little pillar.

Use of the Pentagraph. 1. To copy a design in the same scale as the original. Screw the worm c into the table; lay a paper under the pencil d now placed at f; and the design under the point e now placed at g; then conducting the point over the several lines of the design, the pencil f will draw the same on the paper.

2. If the design is to be reduced into a half, &c. the worm must be placed at the end of the long ruler d, and the paper and pencil in the middle. In this situation conduct the bras point as before, and the pencil will draw its copy in the proportion required, the pencil here moving through half the length that the point does. On the contrary, if the design is to be enlarged one half, the bras point, with the design, must be placed in the middle at c, the pencil and paper at the end of the long ruler, and the worm at the other.

2. To enlarge and reduce in other proportions, there are holes drilled at equal distances on each ruler; namely, all along the short ones, and half-way up the long ones, for placing of the bras point, pencil, and worm, in a right line therein; that is, if the piece carrying the point be put in the third hole, the two other pieces must be put in its third hole. If then the point and design be placed at any hole of the short ruler, which forms the angle therewith, the copy will be less than half the original. On the contrary, if it be placed at one of the holes of that short ruler which is parallel to the long ruler, the copy will be greater than half the original. Few of these instruments will do anything but straight lines, and many of them not even those.