Accession No


Brief Description

prototype navigation computer, instrument for solving spherical triangles, particularly for ascertaining longitude, by Henry Hughes and Son Ltd., English, 1935 (c)


England; London


Henry Hughes and Son Ltd.



Earliest Date

Jan. 1, 1935

Latest Date

Dec. 31, 1935

Inscription Date


metal (brass, wire); wood (mahogany); enamel; plastic (Bakelite); cloth


closed: 325mm width, 365mm depth, 333mm height

Special Collection


Purchased from Charles Miller Ltd. in November 2021.


H. H. & S. LTD.

Description Notes

Prototype navigation computer, by Henry Hughes and Son Ltd., English, 1935 (c)

The unpainted and black painted brass instrument is made up of a circular base with four semi-circular parts at different angles, making it almost hemispherical. It includes a semi-circular scale is marked for North declination, an hour angle with micrometer setting, altitude and azimuth, and an optical illuminated eyepiece, set on a semi-circular articulating guide on a revolving circular base. It has a switch, lamps, a cable, and a plug. The whole instrument sits on a removable wooden plinth, secured with clips, with a drop on/hinged lid, secured with clasps and with a leather carrying handle (broken).




Before the advent of GPS, finding your location at sea could be tricky. One method was to observe celestial objects like the sun, moon, and stars in order to calculate your position using trigonometry. But because both the surface of the earth and the celestial sphere are curved, this requires the use of ‘spherical trigonometry’. This instrument was designed to help with this process, specifically to solve the ‘navigational triangle’, or PZX triangle—a spherical triangle made up of three reference points (P, Z, and X). American inventor E. J. Willis had designed a similar, more complex instrument and there was competition between firms to perfect it. This one appears to be Henry Hughes and Son’s attempt at making a working instrument, but a practical design does not appear to have made it to market, perhaps due to its mechanical complexity and cost.
Created by: Morgan Bell on 22/12/2021


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