During my time helping to organising the seminar series
“Things: Material Cultures of the Long Eighteenth Century” over the course of the last academic year, the idea of the ‘object’ as an important historical source has started to affect my own PhD work.
Recently I’ve been attempting to find out more about the Board of Longitude’s sponsorship of gravity research in various voyages of discovery in the post Napoleonic period. The instrument of choice for this research was the pendulum, as the frequency of its period would vary with the local strength of gravity. The pendulum as a scientific instrument underwent a transformation in this period. From a trusted source of time intervals in astronomical regulator clocks, as it ticked and tocked in the centre of observatories across the globe, into a more problematic instrument when used to measure gravity, encountering problems of air resistance and suspension. My research traces this adaption of the pendulum as they were, sometimes literally, removed from clock cases and swung to measure gravity variation, instead of constant time, and estimate the shape and density of the earth.
One particular instrument, a Shelton Regulator Clock, has jumped out as an object that effectively demonstrates this narrative of increasing complexity for the pendulum as a scientific instrument. There are five Shelton Regulator Clocks that are present in this period and they’ve all claimed to be the one taken with
Cook to observe the 1769
transit of Venus. This confusion between where the five clocks were at different times and for different events is in part a result of an absence of proper cataloguing of instruments owned by the Royal Society and the Board of Longitude to which the clocks belonged. This problem is compounded by the fact that the clocks were stored in the 1780s in a warehouse shared by the two institutions and it would have been easy to confuse them with each other as they’re all similar in appearance. This confusion surround the clocks as a result of their similarity also reminds us that a key element of the 1769 transit of Venus was a lesson learnt from the 1761 expeditions: it was good scientific practise to ensure that your instruments were as identical as possible to ensure the results, taken from different locations across the globe, would be as comparable as possible.
Cook took with him one clock to observe the 1769 transit of Venus, on his subsequent voyages in 1772 and 1776 he took two: a clock from the Royal society and the one owned by the Board of Longitude. The clock that he took with him in 1768 had been previously used by
Nevil Maskelyne to preform gravity experiments and observe the 1761 transit of Venus in St. Helena. This set of gravity experiment was the forerunner to many more experiments resulting in a peak of gravity research in the 1820s and 1830s. Maskelyne report from December 12
th 1771 shows the pioneering nature of this early work – “when compared with the going of the Clock at Greenwich, will shew the difference of gravity from that at Greenwich, which is a very curious point in experimental Philosophy.”
After traveling with Cook the clock was back with Maskelyne, now Astronomer Royal, by 1774 and he took it to Perthshire in order to conduct an experiment to “weight the earth” by measuring the deflection of a plumb line caused by a nearby mountain mass.
George Biddle Airy then took the clock and another from the Royal Society with him to measure the density of the earth at the top and bottom of a mine shaft in Cornwall with
William Whewell in the spring of 1826. The next account of the whereabouts of this clock is in an inventory of the instruments owned by the Royal Society conducted between 1827 and 1834. The inventory includes three Shelton clocks listed as items 33, 34 and 35 that came with a note from Mr Simms, who conducted the survey, saying “The two last employed at the transit of Venus… and Professors Airy and Whewell.” This note tells us that the last two were used by Airy in Cornwall and that Mr Simm’s might not be confident of which, but one of these two clocks, was also the one that had gone with Cook to the Pacific in 1768.
The use of this clock for pioneering gravity experiments by Maskelyne, then traveling with Cook to observe the transit of Venus and finally being used by Airy in Cornwall is an insightful way to map the development of experimental work done with pendulums in both astronomy and gravitational research from the 1760s to the 1820s. The different uses that this clock has had are a fantastic demonstration of the core narrative that I’m attempting to tell as one part of my PhD. This object serves to remind us that it is not only written material that makes history tick, sometimes its clocks.
