Diagonal Gauging Rod Signed J. Long

This boxwood rule has six cylindrical segments with brass ends that can be screwed together to form a total length of 60 inches. One scale on the object measures inches, divided to tenths of an inch. It was used to determine the length of the diagonal of a barrel. The second scale is proportionally divided and numbered from 1 to 400. The user compared the diagonal length in inches to this scale to determine the volume of the barrel in imperial gallons, a unit of measure adopted by the United Kingdom in 1824.

The fifth segment is marked: J. LONG MAKER 43 EASTCHEAP LONDON. The firm established by Joseph Long in 1821 continued to make hydrometers and other instruments after Long's death around 1846. From 1885 to 1936, the firm was located at 43 Eastcheap Street in London.

A leather pouch has pockets for each of the segments. The flap of the pouch is marked: W.

References: Jonathan Cape, A Course of Mathematics: Principally Designed for Students in the East India Company's Military College, 5th ed., vol. 1 (London, 1857), 561; Luke Hebert, The Engineer's and Mechanic's Encyclopedia, vol. 1 (London, 1886), 618–620; Gloria Clifton, Dictionary of British Scientific Instrument Makers (London: National Maritime Museum, 1995), 171–172.

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