Pioneer of Precision

Captain Henry Kater, FRS

Largely forgotten today Captain Henry Kater (1777-1835) conducted pioneering researches in England in the early 19th century to improve the precision of weights and measures. Associated with this was the development of the reversible pendulum for gravity measurements. Kater was actively involved in the Royal Society of London and closely associated with scientists whose names are still familiar today such as Thomas Young, Humphry Davy and William Hyde Wollaston.

When his son Edward died, many of Kater’s relics passed to his other son, Henry Herman Kater, in Australia. Some were presented to Sydney Observatory and the University of Sydney in 1873 and others were dispersed. This display brings together some of these historic relics of Captain Kater’s scientific work for the first time in more than a hundred years.

Sponsored by the National Association of Testing Authorities, Australia, in its fiftieth year.

Who was Captain Kater?

Kater’s name is recalled today by occasional references to Kater’s compass and Kater’s pendulum. The two instruments indicate the interconnected areas of geodesy and metrology in which he made his principal scientific contributions.

Portrait of Captain Kater
Portrait of Captain Kater
Early 20th century copy by Thea Proctor of original in the National Portrait Gallery, London
(Private Collection)

Kater was born in Bristol in 1777, joined the army at 22 and was sent to India where he assisted William Lambton in surveying for the Madras government. After some years he returned to England due to ill health, and was placed on half pay in 1814. Later that year he was elected a Fellow of the Royal Society of London. Kater was active as an officer of the Society as well as engaging in its scientific programs. He was especially engaged in precision measurements relating to the standardisation of weights and measures. In connection with this work Kater devised the reversible pendulum.

He also made a number contributions to astronomy, including devising a method for graduating circles and the inventing the floating collimator. Kater corresponded widely on technical subjects with numerous British and European scientists. He died in London in 1835.

The Royal Society of London

Kater was elected a Fellow in December 1814 when Sir Joseph Banks was near the end of his 42 year reign as President. Kater had already published three papers in the Society’s Philosophical Transactions, and published a dozen or so more there up to 1831.

He served as Treasurer for several years as well as contributing to scientific programs of the Society, notably his pendulum work for which he was awarded the Copley Medal in 1817. He gave the Society’s Bakerian Lecture in 1821 on his researches into the best shape and kind of steel for compass needles.

Kater’s contributions to precision measurement were widely recognised by election to many of the leading scientific societies in Europe and America. He was awarded the Royal Astronomical Society’s Medal in 1831.

Kater’s Convertible Pendulum, 1817

Although suggestions had previously been made for constructing a reversible pendulum, Kater was the first to design and use such a pendulum. The project grew out of a request to the Royal Society to determine the length of a pendulum beating seconds in the latitude of London. The pendulum consists of a bar with a knife edge near each end so that it can be swung either way up. A large cylindrical weight is fixed at one end and a small sliding weight near the other. The position of the small weight is adjusted until the period of swing is the same for each knife edge.

A seconds pendulum is one where the beat (half period) of the pendulum takes exactly one second. It was thought that the length of a seconds pendulum (from the point of suspension to the centre of mass) would provide a basis for reconstructing the yard measure. Using this pendulum Kater determined the length at London to be 39.13929 inches. Because the earth is not a perfect sphere gravity varies between the poles and the equator. Following Kater’s original work extensive pendulum experiments were carried out by Kater and others to determine gravity in many parts of the world, leading to a better understanding of the ‘figure of the earth’.

Science & Society Picture Library, Science Museum, London

A Research Community

Following Kater’s initial work, an extensive program of pendulum research for gravity measurements was carried out by several other scientists including Edward Sabine, John Goldingham, Henry Foster and Basil Hall. This volume contains a series of papers, mainly from the Philosophical Transactions, related to pendulum research.

Bound volume of papers showing: ‘Letter from Captain Basil Hall, R.N. to Captain Kater, communicating the Details of Experiments made by him and Mr. Henry Foster, with an Invariable Pendulum ... from the Philosophical Transactions’, 1823

The title page bears the inscription: "To Captain Henry Kater in token of the Authors regard, & in grateful acknowledgement of those instructions to which alone belongs whatever is exact or useful in this Paper. 13th. Sept. 1823" [Fisher Library, University of Sydney]

Experiments in Madras


John Goldingham read about Kater’s experiments with an invariable pendulum and asked him to send a similar one to Madras. The illustration shows the operation of measuring the swing of the pendulum in comparison to a clock pendulum. The measurements were carried out early in 1821 and quickly sent off for publication in the Philosophical Transactions.

Fisher Library,
University of Sydney

Invariable Pendulum, No. 10, 1827

Having used a convertible (or reversible) pendulum to determine the absolute intensity of gravity at a particular place, an invariable pendulum can be used by comparison to establish the intensity of gravity in other places. A series of 13 invariable pendulums were made - some or all by Thomas Jones - and swung in many parts of the world. Sir Thomas Brisbane conducted pendulum experiments at Parramatta while he was Governor of New South Wales. Pendulum No. 10 was taken on an Atlantic voyage in the 1820s, the Euphrates expedition in the mid 1830s and James Clark Ross’s Antarctic expedition in 1839.

Science & Society Picture Library, Science Museum, London

Case 2: Setting Standards

With greater precision of measurement in the 18th century, the unsatisfactory nature of England’s weights and measures became increasingly apparent. New standard yards were made by John Bird in 1758 and 1760. But it was not until the early 19th century that a Royal Commission was established to report on weights and measures.

Kater was appointed to the Commission along with Joseph Banks, Thomas Young and others. A program of detailed experiments and measurements was carried out by Kater. Using microscopes to compare lengths, he concluded that he could measure to one 10,000th part of an inch.

The report of the Commission led to the Weights and Measures Act of 1824 which introduced Imperial Standards. Subsequently numerous copies of the new standards were required, in which Kater worked closely with several of London’s leading instrument makers.

Line Standard

This bar is stamped with the numbers of inches from 0 to 40, but the only precise basis of measurement is provided by fine lines engraved next to ‘0’ and ‘36’. A hand-written label in the lid of the case states: ‘Value from 0 to 36 inches by mean of 3 sets in different years - 35,998803 inches of the Imperial Standard Yard’. This is signed by Kater and dated 10 June 1830. The bar seems to have been constructed in the mid 1820s.

Presented to the University of Sydney by Henry Herman Kater in 1873
School of Physics, University of Sydney

Line Standard

This bar is inscribed with a longitudinal line crossed by several fine transverse lines at 0, (11.2), 25.6, 40 and 51.2 inches. This provided two 40-inch lengths. The bar is apparently unfinished. Kater was experimenting with different shapes of bar to minimise error.
Presented to the University of Sydney by Henry Herman Kater in 1873
School of Physics, University of Sydney

Line Standard

This triangular bar measures 40 inches between fine lines inscribed on the gold plugs near each end.

Presented to Sydney Observatory by Henry Herman Kater in 1873
Lent by the Powerhouse Museum, Sydney

Reconstructing the Standards

The primary standards of weight and length in England were preserved at Westminster. When the Houses of Parliament burned down in 1834 - an event dramatically captured in two paintings by Turner - these standards were destroyed and new primary standards had to be prepared. Forty bars were cast in 1845 of which one was selected as the primary of the Imperial Standard Yard. Number 18 was supplied to the New South Wales Government in 1855 as the primary standard of the colony. The yard is measured between fine lines marked on a gold pin in the well at each end of the bar. Kater’s work on standards of length in the 1820s provided a significant basis for reconstructing the primary standard.

Lent by the National Measurement Laboratory, Sydney

Case 3: The Instrument Makers

By the end of the 18th century, London was the principal centre for the manufacture of precision instruments in Europe. As an inventor of instruments and in connection with the production of weights and measures, Kater was closely associated with craftsmen specialising in different areas of precision instrument making in the early decades of the 19th century. Among these were T.C. Robinson, R.B. Bate, Edward Troughton, George Dollond and Thomas Jones.

Edward Troughton (1756?-1835)

Troughton was one of the leading makers of precision instruments in London in the early 19th century. He supplied mural circles - an astronomical instrument of his own design - and other astronomical instruments to many of the principal observatories in Britain and abroad. He was his brother’s apprentice and partner. John and Edward Troughton established themselves as specialists in dividing the scales on instruments. With John’s retirement in 1804, Edward continued the business on his own, assisted by a number of workmen.

Troughton was elected a Fellow of the Royal Society of London in 1810. He served on the council of the Astronomical Society from its foundation in 1820, and was elected to several other scientific societies in Britain and abroad. Troughton took William Simms into partnership in 1826. The firm of Troughton & Simms was a major supplier of scientific instruments until after the First World War. Edward Troughton died in June 1835, only a few weeks after Kater.

Kater and Troughton

The excellence of Troughton’s instruments led to orders from many countries. Sometimes orders took years to fulfil. When the German astronomer H.C. Schumacher had been waiting four years for a sector and other instruments, he appealed to Kater to investigate.

Schumacher, founder of the Astronomisches Nachrichten, established an observatory at Altona in Germany in 1821 and was eager to put the instruments to use: ‘the season passes away, and I am check’d in all my operations by Mr Troughtons unaccountable delays’. Kater and Troughton were well acquainted. The previous year Kater arranged for the novelist Maria Edgeworth to visit Troughton.

Letter, Schumacher to Kater, 8 August 1823 - Rare Books and Special Collections, Fisher Library

George Dollond (1774-1852)

Trained as a mathematical instrument maker, George Huggins changed his name when he entered into a partnership with his maternal uncle, the famous instrument maker Peter Dollond. George Dollond himself was respected as a highly skilled optical instrument maker. He invented a number of instruments for astronomy and meteorology.

Dollond was on friendly terms with many of the leading scientists of his day and was prominent in some of the principal scientific siocieties. He was elected a Fellow of the Royal Society of London in 1819 and was an active participant in the founding of the Astronomical Society the following year. Ten years later he was an original member of the Royal Geographical Society.

Russian Standards

Kater had been commissioned to prepare a set of standards for the Imperial Russian Government. The standards of length were made by George Dollond. In his letter of December 1831, Dollond apologises for the delay in completing the order. The lengths were made in iron rather than the more usual brass.

Dollond had found ‘extreme difficulty ... in getting proper workmen to make them in Iron’. He also noted that changes in temperature produced a difference in the comparative lengths of the iron standard and his own brass scale. For his work in superintending the preparation of weights and measures for the Russian Government, Kater received the Order of St. Anne.

Letter, George Dollond to Kater, 16 December 1831
Rare Books and Special Collections, Fisher Library

Azimuth Compass

In 1811 Kater devised this type of compass with a mirror for reading the scales at the same time as observing a distant object through the sighting vane. The following year, the instrument maker Schmalcalder devised a prismatic sight which was soon applied to compasses.

The compass shown here is possibly an original prototype. The inscription ‘H. Kater, Invt.’ is hand written in ink. The scale is also hand inscribed, the numbers being reversed so that they can be read in the mirror. Subsequently Kater compasses with printed cards were made by Thomas Jones.

Lent by the Powerhouse Museum, Sydney

Compass Needles

Kater conducted experiments on different steels and different shapes of compass needles. The results were reported in the Royal Society’s Bakerian Lecture in 1821, and subsequently published in the Philosophical Transactions of the Society. Kater concluded that the best shape for a compass needle was a pierced rhombus. Compasses with broad pierced needles were subsequently made by Thomas Jones.

Fisher Library, University of Sydney

Thomas Jones (1775-1852)

Thomas Jones learned the instrument-making trade from the leading craftsman of his day, Jesse Ramsden. After setting up his own business he established a reputation especially for the large astronomical instruments he supplied to several observatories.

Jones’s association with Kater was a long one. Jones constructed compasses to Kater’s designs as well as pendulums for gravity research. Kater communicated Jones’s innovations in instruments to the Royal Society before the latter was elected a Fellow in 1835.

Azimuth Compass

This Kater’s compass was made by Thomas Jones about 1821. Sir Thomas Brisbane purchased it to use at the observatory he set up in the grounds of Government House at Parramatta. It was subsequently purchased from Brisbane by the New South Wales Government along with other equipment at Parramatta Observatory.
[The compass has a pierced needle similar to one illustrated in the Bakerian Lecture]

Lent by the Powerhouse Museum, Sydney