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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"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

PROBL. III. Having the Rhumb, and the Distance that the Ship hath run upon that Rhumb, to find the Difference of Lon∣gitude and Latitude.

The Analogie or Proportion.

As the Radius is to the Distance run;

So is the Sine of the Rhumb to the Difference of Longitude:

And

So is the Co-sine of the Rhumb to the Difference of Latitude.

So the Rhumb being 70 degr. 1 min. that is E. N. E. 2 degr. 31 min. Easterly, and the Distance run 117 Leagues, the Dif∣ference of Longitude will be found to be 5 ½ degr. and the Difference of Latitude 2 degr.

Ʋpon the Chart.

UPON the Point A protract an Angle of 70 d. 1 m. as the Angle E A F, and draw the Line A F, which is the Rhumb upon which the Ship sailed. Upon this Line set 117, the number of Leagues that the Ship sailed from A to F. Then through the Point F draw the Line F E parallel to A D. So shall E F be the Difference of Longitude, 5 d. and an half, and A E the Difference of Latitude, 2 degr.