The lost theodolite

While researching the Royal Society’s collection of scientific instruments, I’ve come across conflicting accounts of what happened to ‘Ramsden’s Great Theodolite’, commissioned by the Society in 1784. It’s sometimes confused with the Board of Ordnance theodolite, manufactured a few years later and now on display in the Science Museum, and although there are accounts of a theodolite being destroyed when the Ordnance Survey headquarters were bombed in 1940, this is often described as a later device.

Jesse Ramsden, by Robert Home, ca.1772 (RS.9553)

The great theodolite was designed and constructed by Jesse Ramsden FRS (1735-1800) between 1784 and 1787. An enormous and extremely accurate instrument, it was produced for the Anglo-French Survey, a project to confirm the relative positions of the Greenwich Observatory and the Paris Observatory, by linking the two through a large-scale trigonometric survey.

Ramsden’s Great Theodolite appears as ‘Instruments and apparatus belonging to the Royal Society, number 53’ in a list compiled in 1834 (MDA/H/1/9)

The theodolite was part of a set of instruments that Ramsden manufactured for William Roy FRS (1726-1790), who organised the survey under the auspices of the Royal Society. This collection also included a 100-foot steel chain, a small telescope and three glass rods which were all used to measure a five-mile baseline at Hounslow Heath.

Our archives include Roy’s ‘rough estimate’ for the costs of the whole survey, including £200 for ‘Mathematical instruments of the best kinds’. He had appointed Ramsden, as Britain’s leading-instrument maker, to create this equipment, but as his bills started coming in it quickly became apparent that Roy had drastically underestimated the costs.

The expenditure accounts for the survey record a payment of £340 in 1784 as ‘cash paid to Mr Ramsden for Instruments’ followed by another payment of £444 in 1787. The gap of three years shows the time it took Ramsden to manufacture the great theodolite, by which point King George III had arranged a £3,000 fund for the survey.

Roy was quite frustrated by this extended timeline, writing of Ramsden in a February 1787 article in Philosophical Transactions that ‘this ingenious artist was perhaps in the outset too remiss and dilatory’. Ramsden defended himself against these claims ‘from a Gentleman with whom I considered myself in friendship’ in a letter to the Royal Society in May 1787, and finally delivered the finished instrument at the end of July.

The theodolite worked perfectly and by November, when worsening weather thwarted any further transportation of the instrument, there were just two sites remaining for angles to be measured from. Roy returned the theodolite to Ramsden, who couldn’t help but make a few improvements over the winter, and in August 1788 it was used again for the final measurements. With the survey complete, the Royal Society arranged for a warehouse in Bermondsey Street to be fitted up for storing the theodolite.

From the outset, Roy had hoped this project would be the start of a complete trigonometric survey of the whole of the British Isles. When he died in 1790, shortly after sending his final report of the Anglo-French Survey to the press, his cause was taken up by the Master of the Board of Ordnance, Charles Lennox FRS, 3rd Duke of Richmond (1735-1806). Richmond appointed Edward Williams and William Mudge FRS (1762-1820) as Directors of the new Ordnance Survey agency in 1791.

For the Principal Triangulation of Britain, Richmond purchased from Ramsden a new great theodolite, previously commissioned by the East India Company and therefore already complete in 1791. As the survey progressed, the Royal Society also agreed to lend its theodolite for the project. A letter from February 1799 discloses the terms of this loan, with the Ordnance Survey agreeing to ‘repair any damage that may happen to the instrument or in case it should be destroyed, or rendered useless, during the time Capt. Mudge has the charge of it, they will replace the Instrument with a new one similar in all respects.’

R.H. Crew, Secretary to the Ordnance Board, assures the Royal Society any damage to the theodolite will be repaired (MM/3/63)

Both theodolites were then used in parallel for about thirty years, with the RS model returning to our offices in time for the 1834 inventory of instruments and then going back to the Ordnance Survey in 1840 while their version was under repair. It was in storage at the Tower of London when a fire broke out in October 1841 but was rescued from the blaze. The agency then relocated to Southampton, using both theodolites on the Principal Triangulation until the survey was completed in 1853.

From this point our instrument seems to have stayed in Southampton, either in storage or on display. An inventory of our collection from November 1900 does include ‘two Instruments used by Maj.Gen.Roy in the Trigonometrical Survey’ but these are likely the chain and telescope used for the baseline, both now on loan to the Science Museum, rather than the theodolite.

In 1926 Charles Close FRS (1865-1952), a previous Director General of the Ordnance Survey, wrote in his Early years of the Ordnance Survey that the Royal Society theodolite ‘is now preserved at the Ordnance Survey Office at Southampton.’ His photograph shows the theodolite in 1924 with a complete vertical circle, five microscopes for reading the horizontal circle and the telescope’s handle on its left side. This differs from Richmond’s 1791 purchase, now in the Science Museum, which only has four microscopes on the horizontal circle and the telescope’s handle on the right side. The Record of the Royal Society also confirms that it was our instrument that was ‘still in the Ordnance Survey Office at Southampton’ by 1940.

Photograph of the RS theodolite in 1924, from Early years of the Ordnance Survey

Unfortunately, later that year the headquarters of the Ordnance Survey was one of the casualties of the Southampton Blitz, with large parts of the building destroyed on 30 November and 1 December 1940. The fate of our theodolite is revealed in William Seymour’s monumental A history of the Ordnance Survey (1980), where he explains:

‘A distressing and unnecessary loss was the great three-foot Ramsden theodolite used by General Roy in the earliest days of the Ordnance Survey. Before the war it stood in the Library and there had been a whole year in which it could have been taken to a place of safety. Instead it had been removed to the basement of Jubilee Block where it found itself among stores, some of them highly inflammable, and shared their fate.’

Elsewhere he notes that a later Tavistock theodolite employed in the ongoing retriangulation of Great Britain was also lost in the fire, clearing up the confusion over which instrument was destroyed.

So sadly our great theodolite, the first model built by Jesse Ramsden, was indeed melted during the destruction of the Ordnance Survey’s headquarters in 1940. However, from the terms of the original loan, it does appear that they owe us a new one.