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Posted By: Dave Gaddy on: 06/05/2009 07:53:42 EDT
Subject: RE: Making Sense of Re-created Events With Compasses

Message Detail:
Mixing metaphors (or dials), I was thinking of 20 west of north being "twenty minutes to twelve," in clock terms, which I thought of in bearings as an azimuth of five less than due west (270). It obviously wouldn't be safe to pair us in an orienteering course, for the farther we went from the starting point, the farther we'd be apart!

As a long ago Sea Scout (SS Buccaneer), I learned to "box" the compass as North NNE NE ENE E, and could at one time break that down farther, which was done in a manner similar to the refs you've cited, with halves, quarters, etc. Otherwise, I tend to think of that usage as "surveyor's" nomenclature. It might help to eye-ball an actual compass of the type used by the SigC (US) to see how the dial was calibrated. Myer's "Manual of Signals" (1868), pp. 373-4, isn't too helpful, other than to remind the reporting user that reader's of his report won't know in what direction he was oriented, therefore, he should not use "left, right" but "exact bearing by compass" from some location "certainly known to the general." [Wonder if "Curtis house" would qualify?]

Ah, here it is: Pp. 237-238, with illustrations in plate XXIV, opposite p. 226. "The pocket compasses used by signal-officers, are lettered after the plan of a surveyor's compass." "When especial accuracy is required the Prismatic Compass may be used. In addition to the ordinary lettering of this compass, the card [i.e., dial face] should show the lettering of the common suryeyor's compass...that is, with the westerly readings to the right [sic] of the North point, the card being at rest, and the easterly readings on its left." [Good old Myer--should have looked there first!]

It seems that the compass in question (aka "circumferentor") --under Google Books, look for L.E. Dickson's "Plane Trigonometry..." of 1922, and look on p. 93 for illustration of the face -- deals with up to or less than ninety degress to E or W of N. (Nil above 90 degrees used.) Google yields more detailed info. (www dot stanleylondon dot com/compsurv dot htm offers a beautiful brass repro for $55.)

So that pretty well answers my question. The standard, simple pocket compass would have yielded gross directional info, but not lent itself to more precise info for exchange -- it would have been guesstimates. Bearings, to have been relatively reliable (depending on maps) would have required a surveyor's compass. It was essential that the recipient of a 'reading" know (a) where the reporter was located, and (b) his orientation. Example from Sep 62, Jackson's sig man: "my station was on X hill," "my sig flag was up at daylight" [either identifying sta loc or signifying readiness to signal], and "my glass was bearing on Loudon Hgts."

PS: In the modern example you mention, "Kontum" prob intended. ;-)

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