Signedprinted in black on paper label on instrument case: HENRY HUGHES & SON, LTD., Marine Opticians & Manufacturers, 59, Frenchurch St., London, E.C.3. / TELEGRAPHIC ADDRESS: - "AZIMUTH. FEN.," LONDON.
stamped in black on catalog cover: INSTITUTE OF GEOGRAPHICAL / EXPLORATION / HARVARD UNIVERSITY / DIVINITY AVENUE / CAMBRIDGE, MASSACHUSETTS
FunctionFor navigation and taking bearings.
Instructions taken from paper label on instrument case:
"INSTRUCTIONS FOR THE USE OF SIR W. THOMSON'S AZIMUTH MIRROR. / BEARINGS can be taken with this instrument in two ways (1) By looking direct at the object over the top of the prism. The / degrees of the card reflected in the prism are then seen close below the object; (2) By looking through the lens at the / degree divisions of the compass card, and at the image of the objects in the prism, which is seen on the proper degree of / the card. / The first method is applicable to objects on horizon, and is more particularly useful for taking bearings of distant landmarks / which are too indistinct when reflected on the prism. the second method may be used either for taking bearings on the horizon / or for taking bearings of the sun, moon or stars. / For taking bearings by the first method the prism is kept turned (arrow head down) with its mounting stopped against the /
framework. The observer turns the instrument round its vertical axis, till the prism and lens are fairly opposite to the object, / and places his eye so as to see the object over the prism, and reads the bearing of the object from the compass card as seen / reflected in the prism. / For taking bearings by the second method the observer looks through the lens at the degree divisions of the compass card, / and turns the prism (arrow head up) round its horizontal axis, till he brings the image of the object to fall on the card. He then / reads directly on the card the compass bearing of the object. / The pointer is used merely as an aid in directing the instrument towards the object, but the bearings is read directly from the / object is seen on the compass card. It is not necessary the pointer should pointing exactly towards the object, unless the / altitude is very high. For objects from horizon up to 38° of altitude, the error on the bearing would be less than half a degree, / even if the pointer were pointing 4° degrees away from the object."
Primary SourcesHenry Hughes & Son, Ltd. HUSUN Dead-Beat Compass, date unknown (copy in instrument file.
ProvenanceInstitute of Geographical Exploration, Harvard University. Acquired by David Wheatland in 1957.