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File:Leybourn(1700)-(6).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).
Permission
(Reusing this file)
This image is licensed under a Creative Commons Attribution-Share Alike licence, which gives you permission to freely use the image for any purpose, so long as you attribute it as requested here, and make any modified versions of it available under an identical license. If you want to use this image under a different license, for example if you can't give attribution or if you can't share a derivative work under the same licence, then please get in touch.

If you use this image outside of the Wikimedia projects, then I'd appreciate it if you would let me know. Though this isn't compulsory, it seems only fair . Thanks!

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Date/TimeThumbnailDimensionsUserComment
current11:11, 26 July 2015Thumbnail for version as of 11:11, 26 July 2015744 × 1,052 (59 KB)ClemRutter

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