Decoding Harrison

Richard mentioned in his recent post, Looking for a New Harrison, the three accurate longcase clocks that were made by John and James Harrison in the latter half of the 1720s and it prompted me to post a little about an ongoing museum research project that investigates Harrison’s unusual mechanical approach to the pendulum clock.

Harrison claimed that his wooden clocks would keep time to within a second in a month, which for the 1720s was way ahead of the capabilities of the best London-made clocks, such as those made by George Graham.


Harrison recounts his first meeting with Graham in his convolutedly titled book, A description concerning such mechanism as will afford a nice, or true mensuration of time; together with some account of the attempts for the discovery of the longitude by the moon as also an account of the discovery of the scale of musick, thus: “Mr Graham began, as I thought it, very roughly with me, and the which had like to have occasioned me to become rough too; but, however we got the ice broke … and indeed he became as at last vastly surprised at the thoughts or methods I had taken, or had found occasion to take, and as thence found reason enough to believe that my clock might go to a second a month” It is intriguing that Harrison achieved such precision yet his methods made no measurable impact on the practice of making precision pendulum clocks in London or elsewhere. Graham remained a friend and valuable ally to Harrison for the remainder of his life (d.1751), but continued making astronomical clocks in the same manner with the dead beat escapement and heavy pendulum bob with small arc of swing. The principal advantage with Harrison’s design is that he obviated the need for oil by careful use of lignum vitae, paired anti-friction wheels that provided rolling contact for the bearings and the grasshopper escapement, which operates best with a much larger arc of swing. The animal oils used in the 18th century, such as neats’ foot oil, were the Achilles heel of any mechanical timekeeper. Not only were these oils prone to degrading and losing their ‘slippiness’, they thickened in colder conditions and, when warm, thinned and  tended to run  away from the parts that needed lubrication. H1 Harrison’s clocks were free from these unpredictable problems and so offered greater stability in the long term, which is prerequisite for any navigational timekeeper that would be depended on at sea for months at a time. The first timekeeper, H1, is in effect a portable version of Harrison’s pendulum clock with helical springs providing artificial gravity for the twin balances that replaced the pendulum. From the last line of Harrison’s 1730 manuscript, it is apparent that he saw his pendulum clock technology as part of the longitude solution, describing how mariners could navigate using a timekeeper to sail to “where there is another fix’d clock”. This vision was, in a sense, materialised with the proliferation of time ball signals across the globe in the nineteenth century providing accurate time by which the rates of chronometers could be checked. Though the clocks used to broadcast these signals followed Graham's mechanical format and required daily correction by astronomical observation or telegraphic time signal.

Harrison Marine Timekeeper Number Three.  1757

At around the same time as commencing work on H3, Harrison started to construct the pendulum clock that is now known as the ‘Late’ or ‘R.A.S.’ regulator, which is ostensibly the subject of the aforementioned book, written in 1775. With its silvered dial and brass and bronze components the clock departs from the rustic appearance of the earlier wooden clocks, but was never fully completed in Harrison's lifetime. In the book, he made a critical remark about Graham’s dead beat escapement, saying, of George Graham, that

“…either he must be out of his Senses, or I must be so!”  Later in the same publication he stated of his own clock that “…there must be then more reason…that it shall perform to a second in 100 days…than that Mr Graham’s should perform to a second in 1.” 

Keeping time consistently to within one second in 100 days was a degree of accuracy not achieved by mechanical clocks such as Shortt’s free pendulum system. Shortt’s free pendulum was enclosed in a vacuum tank to avoid the irregularities introduced to timekeeping by barometric changes. John Harrison approached the problem differently and rather than protecting the pendulum he deliberately made it more susceptible to barometric change to enable the complex compensation system.

The book is vitriolic and virtually impenetrable, but does contain scattered descriptions of his mechanical approach. On reading the book, the celebrated watchmaker Thomas Mudge, stated of Harrison that the book’s contents had

“…lessened him very much in my esteem…” and that “…there are several things which he says about Mr Graham’s pallets and pendulum that are absolutely false… ”.

The London Review of English and Foreign Literature described the work as “one of the most unaccountable productions we ever met with” and went on to say that “every page of this performance bears marks of incoherence and absurdity, little short of the symptoms of insanity”. Harrison’s book did him no favours.

The astonishing claim was not taken seriously by any of his contemporaries and his radical mechanical approach remained largely unexplored until the 20th century. Then, in 1977, a number of horological scholars, who became known as The Harrison Research Group, began to look at his theories afresh. Amongst this group was Martin Burgess, an artist and clockmaker, who set about making two clocks according to the Group’s understanding of Harrison’s specification.  The first of these clocks, known as the ‘Gurney Clock’, has been on public display in Norwich since 1984 and for a time at Upton Hall; the second, its sister clock (‘Clock B’) was recently finished in the workshops of Charles Frodsham & Co. and has subsequently been experimented on at the Royal Observatory, Greenwich, with exciting results.