Dialling, plain, concave, convex, projective, reflective, refractive. Shewing, how to make all such dials, and to adorn them with all useful furniture relating to the course of the sun; performed arithmetically, geometrically, instrumentally and mechanically: and illustrated with sculptures, engraven in copper, comprised in XIV distinct tractates... / [William Leybourn].

  • William Leybourn
Date:
1700
Catalogue details

Licence: Public Domain Mark

Credit: Dialling, plain, concave, convex, projective, reflective, refractive. Shewing, how to make all such dials, and to adorn them with all useful furniture relating to the course of the sun; performed arithmetically, geometrically, instrumentally and mechanically: and illustrated with sculptures, engraven in copper, comprised in XIV distinct tractates... / [William Leybourn]. Source: Wellcome Collection.

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    1 N T R 0 D U C T I 0 N. F, on either fide equi-dillant from the given Point B.-This done^ Open the CompafTes again to any convenient dilfance, (greater than the former) and fetting one foot in the Point E, with the other defcribe the obfcure Arch G G, (over the given point B , as near as you can guefs) _Again, (the CompafTes being fTill open at the lame diftance) Set one foot in the point F, and with the other defcribe another obfcure Arch H H, crolTing th6 former in the point A: So is A, a point found, through which, if you draw a Right Line from the given point B, that Right Line A B, fhall be Perpendicular to the given Right Line C D, and from the point B, which was required to be done: And the Angle ABD, on the one fide thereof, is equal to the Angle ABC, on the other fide) and both of them are Right (or Square) Angles. . Note^ An Angle is always fignified by Three Letters, as a Point is by One: The middlemolt of which Three reprefenteth the Angular • point, as in this Cafe the Letter B--B, being the Angular point, and the Lines A B, and B C the Sides,' containing the Angle B* ‘ P R O B L.. 11. Horv to erelil a Perpendicular ^ when the given Point is in (or near) the end of the given Right Line, iV.iJ?/V^.]'’“I^Here are feveral ways to effed; this; of which I will herd I Blew you only Two, as being the beft. Let A B be a Line given, and from the point A, towards tire end fl; thereof, let it be required to erect the Perpendicular AC.-Firft, Open the CompafTes to any fmall diftance, and fetting one foot in the given point A, with the the other defcribe an Arch (or part) of a Cir- . cle F E D; — And (keeping the CompafTes ftill at the fame diftance) fet one foot in D, and make a mark in the Arch'at E, and fetting one foot in E, with the other defcribe another Arch of a Circle AF G, crofTing the firft Arch in F.— Again, Set one foot in F, and with the other de¬ fcribe the fmall Arch H H, crofling the former in the point C, througli which point C, draw a Line from the given point A, and that Line fhall be Perpendicular to the given Line AB, and drawn from the point. A, as was required. A Second Waj, ’ Let B (the extreme end of the given Line) be the point given.-- Open the CompafTes to any convenient diftance, and fetting one foot in B, pitch down the other foot at adventure in the point K; fo one foot refting in K, turn the other about till it crofs the given Line A B in L, and draw the Right Line L K at length, and^ fet the fame diftance K L, (at which the CompafTes already ftand) from K to M ; fo a Line drawn from B through M, fhall be Perpendicular to AB, and from the given point B, as was required.
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