Nine geometricall exercises, for young sea-men and others that are studious in mathematicall practices: containing IX particular treatises, whose contents follow in the next pages. All which exercises are geometrically performed, by a line of chords and equal parts, by waies not usually known or practised. Unto which the analogies or proportions are added, whereby they may be applied to the chiliads of logarithms, and canons of artificiall sines and tangents. By William Leybourn, philomath.

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Title

Author

Leybourn, William, 1626-1716.

Publication

London :: printed by James Flesher, for George Sawbridge, living upon Clerken-well-green,

anno Dom. 1669.

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http://name.umdl.umich.edu/A48344.0001.001

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"Nine geometricall exercises, for young sea-men and others that are studious in mathematicall practices: containing IX particular treatises, whose contents follow in the next pages. All which exercises are geometrically performed, by a line of chords and equal parts, by waies not usually known or practised. Unto which the analogies or proportions are added, whereby they may be applied to the chiliads of logarithms, and canons of artificiall sines and tangents. By William Leybourn, philomath." In the digital collection Early English Books Online 2. https://name.umdl.umich.edu/A48344.0001.001. University of Michigan Library Digital Collections. Accessed June 17, 2024.

Pages

II. To find the Variation by the Azimuth.

SUppose the Sun's Azimuth found by the Eleventh Propositi∣on to be 107 degr. 30 min. from the North, and when I set the Compass, I find the Magneticall Azimuth to be 102, the dif∣ference between the true and the Magneticall Azimuth being 5 d. 30 m. which is the Variation.

Now to know whether this Variation be towards the East or towards the West: seeing by the Azimuth found the Sun should have been 107 d. 30 min. from the North, which is 17 degr. 30 min. from the East; but setting of the Sun with my Compass, I find that it was from the East to the Southward onely 12 degr. so that the Degree upon which the Sun should have been was more towards the Right-hand then the Degree on which it was; therefore I conclude the Variation to be 5 degr. 30 min. Easterly.