POWERHOUSE COLLECTION

Henry Kater's 40 inch standard bar

Object No. H9919

Why is this bar triangular, with two gold plugs in it? In 1820 British army officer Captain Henry Kater made precise measurements (to a millionth of an inch) to compare this bar with others, with the aim of creating an official length standard for the British Empire. He chose a triangular rather than flat bar to minimise thermal expansion. He chose gold for the plugs because it is soft and inert, and he used a microscope to position the lines he inscribed on the plugs 40 inches apart. Philosophical Magazine and Journal, vol 58 no 279,1821, pp 281-298 and pp 335-341. Debbie Rudder In the early 1800s, the inconsistency and inaccuracy in measurement standards between Britain and the colony of New South Wales plagued import and export industries. Taxes on the importation of goods were heavily affected by these inaccuracies in measurement. Neither Britain, nor the colony, had a uniform standard of measurement, and weights and lengths were measured differently throughout both countries. This standard measure was used by Captain Henry Kater in the adjustment of the imperial standard measures of Great Britain. Kater was an English physicist and inventor. In 1814 he was elected a Fellow of the Royal Society of London, where he took a special interest in the design of standard weights and measures. He worked alongside Sir Joseph Banks and Thomas Young to experiment with measures and weights and devise methods of taking accurate measurements In 1824 Britain streamlined its measurement standards to the use of just three main terms: the imperial yard, the imperial Troy pound, and the gallon. Brass standards were made to represent these measures, and replicas were distributed to the colony. Kater worked closely with London's most significant scientific instrument makers to produce copies of the new imperial standard, which he had helped dictate. Kater also made a number of contributions to astronomy, including devising a method for graduating circles and inventing the floating collimator. He was also widely acclaimed for his work determining the best kind of steel and form for compass needles. This standard measurement bar was donated to Sydney Observatory by Henry Kater's son in 1873. The Observatory has a long history of assisting Australia to keep accurate time and accurately measure distances. This standard bar remains of national significance due to its pioneering role in Australian and British science and its association with Australia's earliest surveyors, scientists, and astronomers. Reference: Jan Todd, For Good Measure, the making of Australia's measurement system, Allen and Unwin, Australia, 2004 pg 27 http://www.measurement.gov.au/ Holland, J., 'Pioneer of Precision; Captain Henry Kater, FRS', http://www.usyd.edu.au/museums/whatson/exhibitions/kater1.shtml Macmillan, D. S., The Kater family, 1750-1965, The Kater family?, Sydney, 1966 Holland, J., 'Pioneer of Precision; Captain Henry Kater, FRS', http://www.usyd.edu.au/museums/whatson/exhibitions/kater1.shtml Lomb, N., 'Earnshaw's Excellent Timekeepers', in Davison, G., Webber, K., 'Yesterday's Tomorrows; the Powerhouse Museum and its precursors 1880-2005', Powerhouse Publishing, 2005 Forwarded to H. M. Secretary of State by Despatch, No. 141, 1847, Federation and Meteorology, http://www.austehc.unimelb.edu.au/fam/1541.html Written by Erika Dicker Assistant Curator, November 2007.