Public Lectures for the Session 2000-2001 held in Room E7 of the Renold Building, UMIST.
Delivered to the Manchester Astronomical Society

16th November 2000

'The Towneley Clocks at Greenwich Observatory'

Professor Alan Smith
University of Salford (retired).

The northwest is particularly fortunate in having a strong astronomical legacy stretching back to the 17th century. The names of Jeremiah Horrocks and Crabtree are well known in connection with the first ever observation of a transit of Venus across the face of the Sun in 1639. Less well known are William Gascoigne, of Leeds, the inventor of the eyepiece micrometer and telescopic sight and Richard Towneley, of Towneley Hall, Burnley, whose interests included astronomy, clock making and the weather.

In 1675, the founding of the Royal Observatory at Greenwich by King Charles II was largely at the instigation of Sir Jonas Moore, Surveyor General of the King's Ordnance and a friend of Towneley. He advocated the appointment of John Flamsteed, the son of a Derby brewer, as the first Astronomer Royal and helped furnish him with instruments for the new Royal Observatory. The purpose of Greenwich Observatory was the precise determination of stellar positions in the compilation of star tables that would allow accurate navigation, so important to our seafaring nation. This meant the precise timing of stars as they transited the meridian; the validation of the Equation of Time; and the validation of the earth's constant, isochronal, rate of rotation.

Flamsteed was a regular visitor to Towneley Hall, which boasted a fine astronomical library, and wanted Towneley to help him prove that the earth rotated at a constant speed. In the late 17th century this was not accurately known yet was fundamental to positional observations. These demanded reliable time standards and to this effect, Jonas Moore, at his own expense, commissioned the London clock-maker, Thomas Tompion, to construct two astronomical clocks regulated by a novel escapement designed by Towneley

In 1999, an exhibition at Townely Hall presented Prof Smith with the opportunity of building a replica of the Tompion clocks. As an expert horologist, he fashioned the clock in his home workshop at Worsely, based on accurate drawings and descriptions of the originals and was able to recreate the same hand-made escapement and gear train designed over two hundred years ago by Towneley. These were quite novel: for instance, it wasn't until the 1950s that it was learned that the regulating pendulums for the Greenwich clocks, hidden from view behind the wainscoting of the observatory walls, were 13-feet long giving a two-second dead-beat with amplitude of little more than half an inch. This slow beat resulted in the second hand revolving once in two minutes, the minute hand revolving once every two hours and the hour hand, moving as normal, two revolutions per day. This allowed an observer to accurately time a transit against what might be thought of as a magnified dial, thus giving very accurate timings, indeed.

The replica clock was illustrated by many slides and will eventually be accommodated into a re-modelled room at Towneley Hall and, along with a modern sundial designed and to be constructed by Prof Smith, will serve as a lasting memorial to Richard Towneley. The lecture was rounded off with slides of various sundials designed by Prof Smith.

Synopsis by Kevin J. Kilburn (Secretary)

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