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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Gunter's Scale
From: Gordon Talge
Date: 1999 Jun 03, 7:58 PM
From: Gordon Talge
Date: 1999 Jun 03, 7:58 PM
Wonder if anyone has or has read about the "Gunter's Scale".
I am reading about it in Moore's "Practical Navigator" (1798) and in Andrew
Mackay's "The Complete Navigator" (1807). Very clever device.
I quote from Mackay. "The ruler in general use in navigation, is that known
by the name of "Gunter's Scale". The length of this scale is usually two
feet, and about an inch and a half broad. One side of this scale contains lines
for constructing geometrical figures; and the lines upon the other side are call
"artificial", or "logarithmic" lines, being intended to resolve the questions
in the several sailings, and to perform other mathematical operations."
The scale on side 1 are:
Scales of equal parts
Chords, marked CHO
Rhumbs RHU
Sines SIN
Secants SEC
Tangents TAN
Semi-Tangents S.T.
Longitudes M.L.
On side 2 are:
Sine rhumbs S.R.
Tangent T.R.
Numbers NUM
Sines SIN
Versed sines V.S.
Tangents TAN
Meridioinal parts MER.
Equal Parts E.P.
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The chapter goes on to describe how to contruct a gunter's scale mathematically.
Very very clever device!
It seems that the Gunter's scale is a precursor to the slide rule. You use
it by measuring off distances and values with a pair of dividers or compasses.
The trig functions are defined in an equivalent, but different way, then
they are usually defined today; as lengths of lines rather than ratios
of lengths of lines.
--- Gordon
,,,
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| Gordon Talge WB6YKK e-mail: gtalge@pe.net |
| Department of Mathematics QTH: Loma Linda, CA |
| Notre Dame High School Lat. N 34� 03.1' |
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