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Decoding Harrison

by John

A little bit of history was made last month. So far as I can tell it didn’t make the news but I feel it should be recorded as it marks the culmination of an amazing 300-year story. This is long news.

Decoding Harrison‘ was a one-day conference held at the National Maritime Museum in Greenwich – one event in a year of celebrations marking the 300th anniversary of the Longitude Prize. If you’ve not encountered the story, this was a challenge set by the British Government in 1714 to devise a reliable mechanism for finding longitude at sea. This was an important problem for the British Navy and up to £20,000 was offered to anyone who could provide a practical solution.

The prize was eventually awarded to Yorkshire clockmaker John Harrison for his groundbreaking pocket chronometer H4. The clock, looking much like an over-sized pocket watch, was able to keep very accurate time even aboard ship. It allowed the ship’s navigator to compute his own longitude from knowledge of the time in Greenwich and a local observation of mean solar time.

It was fitting then that Dava Sobel, the writer who brought Harrison’s story to the world’s attention, should chair the day. The conference room was full, around a hundred or so attendees including some important figures in British horology.

The first speaker of the day was the museum’s curator of Horology, Rory McEvoy, who outlined the problem Harrison faced. He explained the physics of pendulums and how pendulum clocks operate. These were the most accurate timekeepers of their day, but their operation is very sensitive to motion. A seagoing pendulum clock was never going to work.

Although Harrison is famous for his clocks his family trade was carpentry. Andrew King spoke of the horological ideas in his early wooden clocks. Harrison was able to reduce ware in key parts by using lignum vitae, a naturally oily wood, to self-lubricate the mechanism. Through his innovations, his clocks were achieving an accuracy of one second in thirty days. In his later years he published a pamphlet that made claims to one second in one hundred days. The validity (or otherwise) of this statement was to form the backbone of the day.

Our story jumps forward 250 years or so to the 1960’s whereupon we meet another Yorkshire clockmaker, Martin Burgess. A lifelong admirer of Harrison, Burgess began construction of two clocks using modern materials but incorporating Harrison’s ideas. Both clocks are beautiful. The Gurney Clock (Clock A) has been in Norwich since the early 80’s and Clock B was until 2009, lying unfinished in Burgess’ workshop.

The next speaker was the new owner and patron of Clock B, Don Saff. He told how he had purchased one of Burgess’ timepieces in New York and had subsequently sought him out in England. During his visit he discovered Clock B and set out to rescue and finish it.

Clock B was taken to the workshops of Charles Frodsham and Co to be completed. Philip Whyte, Roger Stevenson and Martin Dorsch, all from Fordshams, spoke in detail about the restoration process. Harrison had advocated a long pendulum with a relatively light bob. This goes against traditional horological wisdom but is one of several key features found in Clock B. As the mechanism was tuned it became clear that Harrison’s claims were no empty boast. The running was eerily smooth and it was felt that his claim should be tested. Could the 300-year-old ideas of a maverick carpenter allow a clock to lose just one second in one hundred days?

In March of this year the clock was moved to the Royal Observatory in Greenwich where it came into the care of Jonathan Betts. After preliminary tests in the horology workshop, the clock was locked into a glass cabinet on April 1st 2014 and sealed by representatives for the National Physical Laboratory and the Worshipful Company of Clockmakers.

Johnathan Betts with Neville Mascalyne's regulator

Older mechanical clocks are particularly susceptible to atmospheric change. Hot or cold weather will cause them to run fast or slow. Harrison invented a number of ingenious ways to compensate for this including his famous bimetallic strip, a bar composed of complimentary metals that shrink and expand to compensate for each other.

In the session just before lunch Jonathan Betts stepped through the wide range of atmospheric conditions experienced during 100 days of testing. Clock B reacted quicker than a traditional heavy bob pendulum but also stabilised faster. In a nail-biting last few minutes he revealed that Clock B had officially achieved what Harrison had claimed. There was a cheer from the attendees! On the 300th anniversary of the Longitude Prize, the unconventional ideas of its prizewinner had yet again been proved correct.

Time for lunch.

One by one we left the NMM building and trekked up the hill to visit the horological workshop inside the Royal Observatory. It’s a tiny room stacked with history. The radio pips play through the speakers and on the far wall was Clock B, still sealed and in its case. On the wall next to it was Graham no. 3, the same regulator used by Nevil Maskelyne to test Harrison’s seagoing clocks.

Clock B
Seal 1
Seal 2

Returning back to the NMM, Burgess’ colleague Mervyn Hobden spoke about the history of the Harrison Group – a group of Harrison devotees founded in the 1970s to discuss and further the horological ideas of John Harrison. Finally Will Andrewes gave a personal introduction to Martin Burgess, his life and his achievements and then Martin was able to speak.

There’s a lot of Harrison in Burgess. He interrupted, he spoke his mind, and he chastised the attendees. I liked him. He was honest and sincere when he talked about the profundity of Harrison’s ideas and how he had put those into practice in Clock A and Clock B. Sadly the clock beat us and there was no time for a panel but the day ended on a high and a standing ovation for Martin Burgess.

Standing ovation for Martin Burgess

The ideas of a genius clockmaker had been proved correct 300 years later by an incredibly dedicated and talented group of individuals. This was long news.

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glathoppa June 13, 02015 - 5:25 am

Verification of John Harrison’s Claim of One Second in a Hundred Days?

At the time of writing (12th June 2015), numerous accounts of a recently claimed verification of John Harrison’s prediction of the performance of his ultimate land-based precision regulator system (as embodied in his final land-based regulator, popularly referred to as the ‘RAS Regulator’) may, at the time of writing, be found by conducting an internet search using, for example, the words: harrison one second in a hundred days

As described and explained elsewhere on the website soptera.wordpress.com Harrison’s claim (in his 1775 manuscript ‘Concerning Such Mechanism…’, often abbreviated as ‘CSM’, for which see the DOWNLOADS section) was that his precision regulator system should be capable of a mean rate to within one second in a hundred days.

Nothing would please me more than to be able to congratulate those involved in the creation of a modern embodiment of Harrison’s principles, capable of demonstrating his performance claims. Unfortunately, an adequate account of the processes by which those claims have recently been verified is, according to my investigations, not available.

May I remind those involved, together with the horological community, of the following, and ask that the principles therein be followed:

The Scientific Method: https://en.wikipedia.org/wiki/Scientific_method

May I draw particular attention to the paragraphs in the above link entitled: ‘Replication’, ‘External review’ and ‘Data recording and sharing’. In short, what is undoubtedly necessary is a detailed account of the dimensions, materials and processes involved in the creation of the test regulator, a detailed description of the methods of setup and adjustment of the test regulator and a through account of the test environment, test equipment and test methods.

Regarding test equipment, particular attention must be paid to the extent to which the test regulator was exposed to variations in the ‘natural atmosphere’ (by which phrase I mean the Earth’s free atmosphere, external to the test building). Further attention must be paid to explaining the degree of sealing of the case from pressure and temperature variations in the ‘natural atmosphere’ and the extent of variation imposed upon the temperature of the ‘natural atmosphere’ (e.g. by any man-made heating system, such as hot water radiator(s) to the test area, amongst many other possibilities). I would expect that heating by sunlight would have been carefully eliminated, although confirmation would be included in any thorough explanation of the test area. I have assumed that variations in the pressure of the ‘natural atmosphere’ are transmitted with little, if any, delay to the test area, although confirmation would also be included in any thorough explanation.

May I also emphasise that, in CSM, Harrison includes a statement that two regulators are necessary for correct adjustment of his ultimate land-based regulator system. Any account of the recently conducted setup, adjustment and test methods should therefore include an explanation of the means by which this requirement was eliminated.


David Heskin July 22, 02018 - 9:15 am


John ‘Longitude’ Harrison (1693-1776)
Exploring the Science of a Precision Timekeeping Pioneer

Adjusting Harrison’s Precision Regulator System – updated post, 21st July 2018

A fairly recent but undated article by Mr J Betts: ‘Harrison’s Barometric Compensation’ describes the influence of circular suspension cheeks and suspension spring material and/or thickness and/or heat treatment upon claimed compensation for barometric error. In compensating for barometric variations, Mr Betts concludes that arc compensation for temperature variations is degraded.

A thorough explanation of this behaviour and/or a suggested solution are/is not given.

Perhaps this demonstrates the problems created by attempting to adjust a single Harrison regulator in isolation, rather than one of an identical pair of regulators, as Harrison clearly suggested.

Regardless of the above, it seems to be obvious (to this observer at least) that the increasing impulse of both the entry and the exit sides of the grasshopper escapement, from the start (pallet nib locking corner capture) to the end (pallet nib locking corner release) will affect pendulum motion in a similar (although, perhaps significantly, not necessarily the same) way as the effect of circular arc profile pendulum suspension cheeks, located to either side of the pendulum suspension spring. By altering the mean increase in impulse delivered by the escapement, pendulum motion will, quite obviously, also be altered. Such an influence upon a precision regulator system declared to maintain a mean rate to within one second in a hundred days (as Harrison claimed) cannot possibly be ignored. Nor, indeed, can a related Harrison statement in CSM be ignored, for he clearly declares (from my “translation” at soptera.wordpress.com):

‘’And now, if the Royal Society please, I will shew them the Draught of the Clock which I have in great part made… and not only the drawing of the pallets, but also the pallets themselves, in order that they may see at least some reason for what I found from such a design of escapement; not only extraordinary attributes, but the things I’ve discussed already and others besides. The indispensable construction of the pallets (to do their duty as described earlier) is a consequence of a suitable extension to the periphery of the escape wheel and its number of teeth (i.e. for seconds beating, one revolution in four minutes). Otherwise, they could not do their duty with regard to their action upon the pendulum or (expressed another way) contribute to a precise mensuration of time. I’d say that the pallets must be by far the most important thing of all.’

The instruction within Harrison’s declaration that the ‘pallets’ (i.e. the Harrison grasshopper escapement) is ‘…the most important thing of all.’ is perfectly clear. Of all the devices contributing to the success of Harrison’s regulator science, he has inarguably identified his grasshopper escapement as the most significant.

Freedom from all but negligible sliding friction aside, it is also clear that Harrison considered increasing impulse to be an especially important feature of his grasshopper escapement. The logical conclusion can only be that increasing grasshopper escapement impulse must therefore be an extremely important feature, probably the most important feature, of his precision regulator system. In that respect, the duration and magnitude of escapement impulse during recoil is of particular relevance, but has apparently been all too easily overlooked. The escapement thereby compensates, to at least some extent, for certain undesirable influences responsible for inconsistent pendulum motion.

Based upon the above, my view is that the manipulation of pendulum suspension springs was, almost certainly, not what Harrison intended for the optimisation of his ultimate land-based precision regulator (The RAS Regulator). This view is reinforced by a revealing CSM statement that he used a very thin pendulum suspension spring, made from an alloy of gold and copper, hammered to ‘thinness’. He mentions that such a spring will be more elastic than when alloyed with silver, thereby suggesting that stiffness is undesirable. In disagreement with Harrison’s statements, Mr Betts’ article attaches great significance to the relatively significant stiffness of the spring.

In summary, pendulum suspension spring stiffness should be minimised, but is otherwise irrelevant to Harrison’s land-based precision regulator science, whereas manipulation of the magnitude of the grasshopper escapement mean end/start ratio is (to use Harrison’s phrase) by far the most important thing of all.

Whilst I’m here, Mr Betts also inludes a section entitled ‘Just one clock?’ which states:
‘It has also been observed that even if this clock really is such a stable timekeeper,it is only one, and its creation might itself also be serendipity. This is a reasonable observation, and one can only encourage others to be made soon, to verify these results if possible.’

I have never expressed an opinion that the Burgess B performance was ‘serendipity’, but have most certainly asked that sufficient information be provided to enable reproduction of the Burgess B regulator, test environment, test methods etc. etc. (see my previous posts herein). Unfortunately, I am still unable to locate any such information, despite Mr Betts’ statement that ‘…one can only encourage others’. If anyone has seen any such ‘encouragement’, however miniscule it might be, I’d be grateful if you could let us all know. Otherwise, the population of the entirety of the planet beyond the RGO remain as distant from scientifically correct verification of the claimed results as they have been for some considerable time.

Censorship | John 'Longitude' Harrison (1693-1776) July 22, 02018 - 11:23 pm

[…] Furthermore, on 22nd July 2018 I submitted my post herein entitled XXXXXXX as a comment on https://computus.org/decoding-harrison/#comment-1782 […]


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