A JOURNAL OF NATURAL PHILOSOPHY, CHEMISTRY, AND THE ARTS. JANUARY 1799. ARTICLE I. Description of a new Inftrument for drawing equidiflant and other parallel Lines with great accuracy and expedition; intended principally for the use of Engravers. With Specimens of its Performance. By W. N. SOME COME months ago I was informed by the Engraver who executes the plates for this Journal, that an ingenious artist had conftructed a machine for ruling the fhades and grounds of copper-plate engravings, which he not only used with great fuccefs in his own business, but had fold to others under an engagement of fecrecy. How far this information might be strictly accurate, was of lefs confequence at the time this converfation took place, than the confideration that it would be easy to make fuch a tool, and render its advantages more general by publication. I then promised to make one; and having now finished it, I take the earliest opportunity of communicating it to the world. From the preceding historical statement, the reader will fee that I have no claim to the original thought of substituting mechanical operation instead of hand work in this department of engraving; and those who have seen the screw gear of Ramfden's great dividing engine will also perceive, that I have done little more than diftribute the parts of this tool in what appeared to me to be the moft fimple and convenient manner. Fig. 1. Plate XX. represents the inftrument of the fize of that which I have made. The outline fection, fig. 2, reprefents the fame viewed in a direction parallel to the edge of the moveable ruler. The letters denote the fame things in both. AAAA is a frame fixed to the drawing-board. It resembles that of a sliding rule, and ferves to guide a fliding piece, which, lying in fig. 1, immediately under the fcrew, could not with convenience be denoted by any letter. BC is a fcrew of exactly forty threads in the inch, but might conveniently be made of a coarfer thread. GH and ED are two cocks, the former of which, GH, is fixed to the frame A, and bears a clip or pair of nuts, which open and shut with a joint like a pair of compaffes, and either embrace the fcrew by a reVOL. II.-JAN. 1799. 3 K gularly |