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Re: Kelvin Hughes sounding sextant !
From: Paul Hirose
Date: 2020 Mar 13, 14:36 -0700
From: Paul Hirose
Date: 2020 Mar 13, 14:36 -0700
On 2020-03-09 9:02, Frank Atkins wrote: > I have just picked up a Kelvin Hughes sounding sextant. Ex Royal Australian navy. Last active check was in 1981. It has no shades just the two mirrors as made. This sounds like a sextant for hydrographic survey fixes via the measurement of angles between points on shore. The procedure is described in Bowditch and also in "Hydrographic Manual," Special Publication No. 143 of the US Coast & Geodetic Survey. The 1928 edition may be downloaded here: https://library.noaa.gov/Collections/Digital-Collections/USCGS-Special-Pubs (A 1942 edition is listed too, but it's only one chapter of the publication.) "Position determination by sextant angles taken on board the sounding vessel is the most satisfactory and most commonly used method for coastal work. Two observers observe angles simultaneously, one between a right-hand object and a center object and the other between the center object and a left-hand object. The position of the vessel is then plotted by using a three-arm protractor to effect a graphic solution of the three-point problem. "Hydrographic sextants resemble those used for navigation but are of lighter construction and are read only to minutes. They can be used to measure angles up to about 140°. The telescope generally has a bell-shaped tube, so as to include as large a field as possible." Also of interest in that book is the special procedure for obtaining celestial fixes of the highest accuracy.
