Page:Philosophical Transactions - Volume 004.djvu/10

 piece E D moving round about the Center E; by which means the Sight may be remov'd either towards R or F.

EF is a Rule fastn'd onto the two Rulers GG, which Rulers serve both to keep the square Frame SSSS perpendicular, and by their sliding through the square holes TT, they serve to stay the Sight, either farther from or nearer to the said Frame; on which Frame is stuck on with a little wax she paper OOOO, whereon the Picture is to be drawn by the Pen I. This Pen I, is by a small Brass-handle V. so fixt to the Ruler HH, that the point I. may be kept very firm, so is alwayes to touch the Paper.

HH. is a Ruler, that is alwayes, by means of the small strings aaaabbbb, mov'd Horizontally, or Parallel to it self; at the end of which is stuck a small Pin, whose head P is the Sight; which is to be mov'd up and down on the Out-lines of any Object.

The Contrivance of the Strings is this. The two Strings aaa, bbb, are exactly of an equal length. Two ends of them are fastn'd into a small Leaden Weight QQ, which is mov'd in a Socket on the back side of the Frame, and serves exactly to counterpoise the Ruler HH, being of equal weight with it. The other two ends of them are fastn'd to two small Pins H. H, after they have been roled about the small ''Pulleys N, MM. LL. KK; by means of which Pulleys if the Pen I. be taken hold of and mov'd up and down the Paper, the Strings moving very easily, the Rule will always remain in an Horizontal'' position,

The manner of Using is is this: Set the Instrument on a Table, and fix the Sight A. at what height above the Table, and at what distance from the Frame SSSS, you please, Then, looking through the Sight A, and holding the Pen I. in your hand, move the Head of the Pin P. up and down the Out-lines of the Object, and the point I. will describe on the Paper OOOO, the Shape of the Object so trac'd.