File:Britannica(1771)-(3a).svg

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Description

This method uses the properties of chords to establish distance in the top quadrant, and then transfers this distance onto the latitude radius in the bottom quadrant so that is established. Again, a transfer of this measure to the chords in the top quadrant. The final lines establish the formula =

It was used in the Encyclopedia Britannica First Edition 1771- Sixth Edition 1823
  • 1: The Gnomon is drawn first against the North South line. In doing so, a diameter at φ degrees to the vertical is drawn- its reflection is needed.
  • 2: The circumference is marked off at 15° intervals in the top quadrants. Chords parallel to the horizontal are drawn (the length of these chords will be 2 sin (Θ/2).
  • 3: The measurement of each chord is transfered to form a scale along the lower radiuses. When joined these points form a series of parallel lines that are sin θ. sin φ in length.
  • 4: These measurements are transferred up to the chord.
  • 5: The final hour lines are drawn from the origins through these crossing points.
Source Own work
Author Photograph by Clem Rutter, Rochester, Kent. (www.clemrutter.net).
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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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current19:45, 18 August 2015Thumbnail for version as of 19:45, 18 August 2015744 × 744 (77 KB)ClemRutter (talk | contribs)

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