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The Description of the Travis-Scale.
The making of this Scale is all one in a man∣ner as you made the former; only the Line of Sines is there but once made, and here the Parts answering each Quarter are twice put down, or in two Lines marked with N. S. which stands for to shew the Line to be Northing, Southing; and E. W. signifies Easting and Westing. The first is the Sine, the second is the Complement that any Point or Quar∣ter maketh an Angle with the Meridian. The Line marked with T. is the Tangent-Rhomb and Quar∣ters, and the first Line is a Line of Numbers, which you have been already shewn to make.
One Example I will give the Learner, notwith∣standing it is so easie; for some there are that will not understand, though they see it often done; yet (to my knowledge) are Mates to good Ships.
EXAMPLE.
Suppose you was to set the first and seventh Rhomb or Artificial Point on the Scale, which is 11 Degrees 15 Minutes, the Equal Parts answering thereunto is 1290; therefore take 129 of your Scale of Equal Parts, and lay it from the beginning upwards, and you have by that distance the first and seventh Rhomb of your Scale.
In like manner do for any other of the Points and Quarters by these Numbers, until you have fi∣nished the Scale; and when you have done, you have an Instrument the most easie, ready, and necessary that I know of, for the working of Travises, and correcting your dead Reckoning, which shall be shewn in the Part of Sailing by the Plain Chard, in the Fourth Book. On the back side of this Scale you may set a Line of Chords and Equal Parts, and Points, for the ready protraction of Angles.