File:Leybourn(1700)-(1).svg

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Summary

Description
English: William Leybourn's method (1669) from The Art of Dialling - commonly quoted from the third edition 1700. It was possibly taken from John Blagraves 1609 book The Art of Dyalling in Two Parts (Book 2 , Chapter 10).

This dial is for the latitude 52° and the dial plate is accurate to within 0.6°.

  • Draw a circle, and its two cardinal diameters- E-W, and S-N (top to botttom). O is their crossing point or origin.
  • Using a Line of Chords or a protractor- lay off two lines 0a that is 52° from OS, and 0b that is 52° from OS. (they will be at right angles. The points a and b are important.
  • With a straight edge draw a line connect E with a, it cuts SN (the meridian line) at P, which is called the Pole of the World. Now connect E to a, it connects AE. This point is important as it is where the meridian crosses the equinoctial circle. The points E, AE, and W lie on the equinoctial circle. The next task is to use this information to locate the centre and to draw the circle. Use a construction line to join AE and W. At the centre point, raise a line at right angles. Where it cuts the SN (the meridian) will be C, the centre of the equinoctial circle. Use C to draw an arc from E to W, it will pass through AE.
  • There is now a semicircle passing through E and W, and the equinoctial arc passing through E and W. Divide the semicircle into 12 equal parts- ie 15° angles. Mark with a "construction point". (blue)
  • A ruler joins O with the points on the semicircle. As these lines cut the the equinoctial arc a series of unequal points ("markers")(red star) are created.
  • A ruler from P (the pole of the world) takes a line from these markers back over the semicircle. Where it cuts it will be the "hour point"- these hour points are unequally spaced.(red)
  • The hour lines are drawn from each of these "hour points" to O the origin. The origin is the foot of the style which is cut at 52°.
Source Own work
Author Photograph by Clem Rutter, Rochester, Kent. (www.clemrutter.net).
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current11:11, 26 July 2015Thumbnail for version as of 11:11, 26 July 2015744 × 1,052 (58 KB)ClemRutter
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