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This section of the website is dedicate to an on-going project, namely, my building a replica of John Harrison's last regulator. The original clock is on display in the Greenwich Observatory, London.


John Harrison’s pioneering work in the field of precision timekeeping is little short of genius. He is largely remembered for his sea clocks H1, H2, H3 and H4, and his endeavour to establish the accurate measurement of longitude. His final project was to build a regulator for the Greenwich Royal Observatory. The clock was never finished as he died before its completion and the science it embodied, disregarded by the horological world, slipped into oblivion.


I am fascinated by the early eighteenth-century science of John Harrison, and in order to understand more fully his genius, I am building a copy of his last regulator. In doing so, I am using traditional clockmaking principles and testing methods that would have been available to Harrison, [with no use of CNC or digitally controlled equipment]. Further, I use identical materials, including his widespread use of bronze and lignum vitae.

Since no drawings exist of his final regulator, the information and dimensions of the clock are drawn from numerous sources, as described below. As the original clock was unfinished, some items are based on conjecture, or the work undertaken by Commander R. Gould in the 1920s.


This last regulator is an example of the ultimate weight driven regulator with a pendulum suspended in free atmosphere. Fortunately, the original clock was rescued from oblivion, and completed in the 1920s by Lt. Cmdr. Rupert Gould. This working clock is housed in the Greenwich Royal Observatory, alongside Harrison’s earlier sea clocks.


In 1775, the year before he died, Harrison published a manuscript titled, “A description concerning such mechanism as will afford a nice, or true measurement of time”. This document summarised his lifetime’s work, embodied in his final regulator, that he claimed would be capable of maintaining a rate of one second in a hundred days. His science has since been proved to be a reality through its application and testing of the Burgess B clock.


The specification of the regulator is truly amazing. No oil is used in the clock and all arbors run on anti-friction wheels mounted on wooden, lignum vitae, bushes, which require no lubrication. The escapement wheel is driven by a 30 second remontoire that equalises the power to the escapement. The escapement is made to Harrison’s unique frictionless double grasshopper design, and the stability of the pendulum length due to temperature change, was achieved through his invention of a gridiron pendulum. Finally, his application of roller bearings for supporting the main winding arbor, is one of the earliest applications of a device now universal in engineering.



Research and sources of information

No drawings exist for the Royal Astronomical Society Regulator and therefore the information for building has been accumulated from a variety of sources.

David Heskin built a working clock based on RAS regulator principles. Although the clock was running it was never completed, and a number of items were altered for manufacturing simplicity. Drawings of his clock are published in his book, ‘Sleeping in Oblivion’.

Stuart Harrison created a set of detailed drawings and published them in book form. However, I am not aware a working clock was ever made from these drawings.


The BHI working party has produced a pair of clocks based on information gathered when the clock was dismantled for servicing. An account of their building programme, containing much useful detail, was published in Journals of the BHI  2013 -2021




The lost science of John “Longitude” Harrison  

W.S. Laycock

The Quest for Longitude - Papers delivered at the Longitude Symposium 1993 Cambridge Massachusetts.  

Edited by J.H.Andrewes

Harrison Decoded   

Ten articles from leading horologists, edited by Rory McEvoy and Jonathan Betts

John Harrison’s Contrivance   

Stuart Harrison

Sleeping in Oblivion  

David Heskin

Time restored   

Jonathan Betts

British Horolgical Journal  

Articles by Colin Ferguson MBHI


Dava Sobel



RAS regulator  David Penny

A Harrison Remontoire  Thomas Bradley 1840


I am grateful for the generous advice from Colin Fergusson MBHI and Peter Hastings.

The original Royal Astronomical Regulator now housed in the Greenwich Royal Observatory


John Harrison 1693 - 1776

In this portrait Harrison is seen holding his final sea clock H4 and, in the background, there is a regulator with gridiron pendulum.

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