Marine Range Finder by Kelvin Hughes

In steam driven days (using the original meaning of the expression) and long before radar, a manual method of calculating distance at sea was essential for safe passage. This intriguing little hand held optical instrument fitted the bill perfectly. It was operated on the same principle as early cameras where a split image rangefinder was built in and when a distant object lined up against both prisms the distance could be calculated from an attached scale and an accurate focus could be obtained.

In operation this instrument would be set by aligning the height of the ships mast against the left edge of the transverse height scale from 0 to 200 feet. This need not necessarily be mast head to waterline measurement as the note pad on the reverse side has provision for noting also the distance from the mast head to the "lower top" and "Upper speed to stern lt." The distant vessel is then viewed through the telescope, where a split field view is seen. The image of the head of the mast in one half is brought alongside the image of the waterline in the other half by rotating the knurled knob on the right of the instrument and when aligned the distance in cables (a cable is one tenth of a nautical mile) can be read against the index on the distance scale.

The instrument is in excellent condition and whilst we can no longer guarantee its accuracy it all seems to function as intended. It carries a makers label to 'Kelvin Hughes A Division of Smiths Industries Ltd'. Kelvin & Hughes Ltd was formed in 1947 by the merger of the scientific instrument manufacturing firms of Henry Hughes & Son Ltd, London, England, and Kelvin Bottomley & Baird Ltd, Glasgow, Scotland. Kelvin & Hughes Ltd were essentially a part of Smith's Industries Ltd founded in 1944 as the successors of S. Smith & Son Ltd. Kelvin & Hughes Ltd was liquidated in 1966 but the name was continued as 'Kelvin Hughes, a division of Smiths Group plc'. We therefore deduce this instrument was manufactured around 1966 or later but the basic pattern was used much earlier by the Royal Navy. Whilst an obsolete instrument today it makes a fine talking point and would sit happily in a marine or scientific instrument collection and represents excellent value at a modest price. Instrument measures 5.25" x 3.25" (13 cm x 8 cm).