The Weird Origin of ‘Chronometer’ and What It Means for Watches Today

Of escapements and 18th-century satire
Source: Hodinkee

Originally published by Jack Forster on Hodinkee. 

Humpty Dumpty famously says, in Alice In Wonderland, that words are nothing more than pieces in a game, where you can change the rules any time you want. "When I use a word," he says, "it means just what I choose it to mean – neither more nor less." To which Alice replies, tactfully if skeptically, "The question is...whether you can make words mean so many different things." In all of watchmaking there's probably no word that this applies more to than "chronometer," which first burst on the scene in 1714 – or so many people think – and has been shape-shifting ever since. 

Now, you don't have to spend much time around watches before you figure out pretty quick that a chronometer is not a chronograph. The latter, of course, is basically a combination of a watch and a stopwatch; the former, at least nowadays, is a watch which – assuming it comes from an ISO-standards compliant country, which Switzerland is – has been certified by an independent examination board and found to meet certain minimum standards.

A modern wristwatch chronometer, manufactured by Rolex.
Source: Hodinkee

That officiating body today is the (in)famous Controle Officiel Suisse des Chronomètres, better known to Watch Idiot Savants the world over simply as the COSC. In its current form the COSC has been around since 1973, but prior to that, testing took place at the so-called Bureaux officiels de controle de la marche des montres, which in horological literature are generally more concisely referred to as the BO agencies. There were different numbers of these at different periods in history; one of the oldest, in Bienne, was founded in 1877. It was these agencies that were responsible for providing independent testing of watches seeking chronometer certification, until they were put under central administration and dubbed the COSC in 1973.

COSC standards for mechanical watches are pretty straightforward. For most watch enthusiasts, the most relevant standard is the one for average daily rate over a 10 day testing period; for a watch to pass, it must maintain an average daily rate of -4/+6 seconds. Rolex used to get flak now and again for calling its watches "superlative" chronometers on the dials, but in 2015, the Crown introduced the new Day-Date 40, along with a new Superlative Chronometer internal certification, requiring a daily rate of -2/+2 maximum per day. In 2016, Rolex announced it would extend this to all Rolex watches moving forwards.

That's the gist of it for the 20th and 21st centuries. In the 19th century, however, as you go back, you start to see the meaning of the word change as you look further and further back at its usage and evolution.

The Chronometer Escapement

Source: Hodinkee
A mid-19th century chronometer escapement pocket watch, by Girard-Perregaux.
Source: Hodinkee

Above is a key-wound, high-grade pocket watch made by Girard-Perregaux for the English market, dating to about 1860. We looked at the technical features of this watch last January, and one of those features is directly relevant to the history of the term "chronometer" (which you can see engraved on the movement dust cover above – with the English rather than French spelling, as this was an English market watch).

A detent escapement, by Girard-Perregaux, about 1860.
Source: Hodinkee

That technical feature is the escapement of the watch, which is what's called a detent escapement. The detent escapement was, as far as we know, invented by French horologist Pierre LeRoy in 1748, although the first practical version of the escapement was the pivoted detent escapement of John Arnold in 1775. Arnold's contemporary in England, Thomas Earnshaw, was responsible for developing the version of the detent escapement that came to be most widely used, and below you can see the basic layout of the spring detent escapement, as it's shown in the 1896 edition of Britten's Clock and Watchmaker's Handbook.

Source: Hodinkee

The way the whole thing works is pretty simple. The escape wheel is kept from turning by the locking pallet (d) which is maintained in place by the flat spring (f). As the impulse roller (b) which is basically the hub of the balance, turns counterclockwise, a jewel close to its center (unlabeled, in the diagram; it's sometimes called the discharging, or unlocking, pallet) contacts the tip of the gold spring (i) making it press on the slightly shorter horn (h) which shifts the detent aside (downward, in the picture). This lifts the locking pallet off the escape wheel tooth, allowing the escape wheel to turn clockwise. As it turns, one of its teeth contacts the impulse pallet (c) on the roller, pushing on it and giving impulse to the balance to keep it swinging. As the impulse pallet disengages with the gold spring, the detent, under the action of the spring (f) flicks back into its original position, just in time for the locking pallet to catch the next escape wheel tooth and re-lock the escape wheel.

On the return swing of the balance, it rotates clockwise; the discharging/unlocking pallet on the balance roller again contacts the tip of the gold spring (i). However, in this case, it lifts the tip of the gold spring up off the horn of the detent (h) allowing the jewel to pass without moving the detent itself. As the escape wheel doesn't unlock on the return swing of the balance, no impulse is given. As you can see, for the whole thing to work, the clearances, as well as the tension of all the springs, have to be very carefully controlled. It's a delicate mechanism and takes a lot of skill to make. The payoff, though, is an extremely precise escapement that's also very efficient. To get a really clear idea how the escapement works I recommend checking out this animation.

Source: Hodinkee
Above, pocket chronometer and movement by John Arnold, 1781.
Source: Hodinkee

The detent escapement came to be called a chronometer escapement, thanks to the use of the word as a designation for a precision watch containing a detent escapement. The very first person to use the word "chronometer" in reference to a watch with a chronometer escapement, seems to have been none other than John Arnold himself, who coined the term "pocket chronometer" in 1782. From that point forward, and for some time, "chronometer" primarily denoted (at least, in English language watch and clock-making) a precision timepiece with a detent escapement. 

As Fritz von Osterhausen points out, however, in Wristwatch Chronometers, "the main characteristic of a chronometer is its precision," and as lever watches gradually achieved very high precision, the term came to mean, by the 20th century, any very accurate watch. Osterhausen writes, "In 1925, the Swiss Association for Chronometry defined a chronometer in the following way: 'A chronometer is a watch which has received a certification from an astronomical observatory.'" Today, almost no one but a few die-hard lovers of antiquated terminology still insist that "chronometer" should only be used to refer to a watch with a detent escapement (which is a good thing for Rolex and Omega and Breitling and a lot of other brands for whom a chronometer rating is a selling point).

So What's The Slightly Weird Part?

Now, for many years, I've been asking other watch enthusiasts if they know who invented the term. As the answer has generally been "no," it's given me a chance to smugly repeat the conventional wisdom, as found in Rupert T. Gould's The Marine Chronometer: Its History And Development (and elsewhere) that it was apparently coined by an English clockmaker named Jeremy Thacker in a pamphlet on the longitude problem which was published in 1714. The funny thing is, information gets easier to find every day and in doing research for this story I started to run across assertions that the pamphlet was a "probable satire" and that, in fact, there may never have been a Jeremy Thacker, horologist and pioneering longitudinarian, at all.

Diagram from Jeremy Thacker's pamphlet, illustrating his proposed vacuum-enclosed sea clock.
Source: Hodinkee

Let's look at the evidence. In 1714 a pamphlet was published, with the author's name given as Jeremy Thacker. Now, given the title of the pamphlet, it's interesting that the possibility of it being a satire didn't occur to someone sooner; the pamphlet is called The longitudes examin'd: Beginning with a short epistle to the longitudinarians, and ending with the description of a smart, pretty machine of my own, which I am (almost) sure will do for the longitude, and procure me the twenty thousand pounds. 

That kind of language already sounds like someone's pulling your leg. Here's a little background.

The first Longitude Act, establishing the £20,000 prize, had been passed earlier that year and Thacker's pamphlet was just one of many, many reactions. As you might expect, the enormous amount of money offered for a solution to the longitude problem brought a lot of cranks out of the woodwork in very short order, and Thacker takes to task several of the more egregious examples of improbable solutions to the longitude problem in his pamphlet. He also used the word "chronometer" for almost the first time it's know to have appeared in print in English. After going to considerable length to describe his ideas for a reliable sea clock, he writes: 

"In a Word, I am satisfy'd that my reader begins to think that the Phonometers, Pyrometers, Selenometers, Heliometers, Barometers, and all the Meters are not worthy to be compared with my Chronometer."

Everyone from Rupert T. Gould, to Dava Sobel (in her bestseller, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time, which first made the general public aware of the longitude problem) seems to have taken at face value the notion that Thacker was a real person, and that his proposal was serious. However, in a 2011 book, Documenting Eighteenth Century Satire: Pope, Swift, Gay, and Arbuthnot in Historical Context, author Pat Rogers makes the claim that Thacker was the invention of a Dr. John Arbuthnot. Arbuthnot was a physician and mathematician, and, most significantly, he was a member of the Scriblerus Club – a group of satirists that included Alexander Pope, and Jonathan Swift.

Scientist, physician, and satirist Dr. John Arbuthnot. Portrait by Godfrey Kneller, 1722.
Source: Hodinkee

I won't go into all the details in depth, but Rogers has done some pretty impressive research in support of the idea. First of all, Jeremy Thacker is absent from any of the records of the time; there's no record of his birth, nor of his having been professionally active; no marriage, children, or obituary. No other written works or correspondence of his exists. (Other authors referring to his pamphlet in later decades and centuries variously described him as a clockmaker, amateur instrument maker, amateur scientist-mathematician, and so on, but there are no sources to support any of that.). 

Second, Swift and other Scriblerus members are on record as having referred to the prize-motivated attempts to win the Longitude Prize as largely absurd, and a ripe subject for satire – Swift once wrote to his friend Esther Johnson, "Do you know what the Longitude is? A Projector (an archaic usage, meaning someone who sets up and plans a project) has applied to me, to recommend him to the Ministry, because he pretends to have found out the Longitude. I believe He has no more found it out than he has found out mine arse."

Jonathan Swift; portrait by Charles Jervas, 1709. National Portrait Gallery.
Source: Hodinkee

Swift and Arbuthnot were close friends – Swift, generally happier than not to satirize anything on two legs, is supposed to have said of Arbuthnot that the only fault an enemy could lay upon him was a slight waddle in his walk. More relevantly, though, Arbuthnot's amiability extended to his being notoriously disinterested in getting credit for his own work and ideas, which lends additional credibility to the idea that he might have been behind the elusive Jeremy Thacker. 

The lack of any evidence of Thacker's existence, as well as the grandiose tone of the pamphlet and its unashamed announcement of the hope of financial gain as Thacker's main motivation, are interesting indications that Rogers may be right, and that the author's intention was satirical. (The pamphlet is also included in an anthology of Arbuthnot's work published shortly after his death, although that source – The Life And Works Of Dr. John Arbuthnot, MD, MRCS – is not considered totally reliable.) Still, the question remains open, and absent something like a birth or death record, we'll probably never know for sure.

The other interesting note to all this, however, is that despite Thacker's coinage of "chronometer" being generally taken as gospel, it's not actually the first known occurrence of the word in English. As it turns out, the earliest the word shows up in print is the year before Thacker's pamphlet – in 1713, in a book by the theologian and philosopher William Derham. Derham was a clergyman, a prolific writer, a very active scientist, a naturalist, and, as it turns out, a clockmaker; one of his works is the Artificial Clockmaker, which is a technical text on the subject. He was familiar with the work of the mathematician, physicist, and horologist Christiaan Huygens (the inventor of the first accurate pendulum clock) and translated some of his works.

The title page of Derham's Physico-Theology, 1713.
Source: Hodinkee

In 1713, he published his Physico-theology, Or, A Demonstration of the Being and Attributes of God from His Works of Creation, which is a look at the world and its inhabitants – human and animal – from a naturalist's perspective. In it, he argues that every feature of the natural world is evidence for the existence of a Creator. The footnotes in the book are extremely detailed – longer than the text proper, in many cases. (His notes on his experiments on animals are kind of hair-raising; he seems to have spent a lot of time putting the Earth's wee creatures in his vacuum chamber and seeing how long it took for them to expire. His asphyxiations of a mole and a bat are described with clinical detachment, and make for exquisitely depressing reading.) However, in the chapter on light and optics, we find this passage:

The first known occurrence of "chronometer."
Source: Hodinkee

"But according to my own Observations made with one of her Majesty's Sakers (a medium cannon in use at the time) and a very accurate Pendulum-Chronometer, a Bullet, at its first discharge, flies 510 yards in five half Seconds, which is a mile in a little above 17 half-seconds."

So there it is – the earliest use I can find anywhere of "chronometer" in the English language. I think it's fair to say, though, that the term probably originated earlier than Derham's book; he uses it as if it's already a well known scientific and horological term of art, and for any educated person of the era, it would have been a natural coinage – the word is derived from ancient Greek roots and means, "to measure time." It may not be that much older than 1713 – there would have been no need for it before precision timekeepers needed to be distinguished from less precise ones, and Huygens' first pendulum clock dates to 1657. 

But you never know. The ancient Greeks had the word "chronograph" as it turns out (χρονογραφεω) although the term meant the keeping of historical records; the ancient Greek for a time-measuring instrument is "chronolabon" (χρονολαβον) literally, something that "takes" the time. This word shows up around 400 AD (in the writings of Proclus of Constantinople, if you're curious) so it's perfectly possible that "chronometer" in the sense of a time measuring instrument, is a lot older than we can discover for now. In modern Greek, χρονομετρο (chronometro) can mean either a timer specifically, like a stopwatch, or a chronometer in the sense of a precision timekeeper, but the word seems not to have occurred in the Classical literature.

The movement of John Harrison's H4 marine chronometer.
Source: Hodinkee

Despite Swift and the other Scriblerus members' conviction that methods for finding longitude were about as intellectually respectable as proposals for perpetual motion machines, Harrison was able to demonstrate a practical sea chronometer only a relatively short time after the 1714 Longitude Act. As a young man, Harrison had finished his first clock in 1713, and by 1761 H4 had made its proof-of-concept voyage to Jamaica, enabling the HMS Deptford to find its longitude with an error of only one nautical mile. And by then, of course, the escapement which would come to be synonymous with the word "chronometer" had already been invented by LeRoy.

It's kind of fascinating to think, though, that the two earliest known uses of the word came from such different contexts. One was a serious text on the evidence for a divine hand in the structure of the universe. But the other, almost-first use of a word that became synonymous with precision timekeeping, and which represents a major marketing point for every brand that uses it today, was in what may have been a satire.

Sources: Fritz von Osterhausen, Wristwatch Chronometers; Dava Sobel, Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time; Rupert T. Gould, The Marine Chronometer, Its History And Development; Pat Rogers, Documenting Eighteenth Century Satire: Pope, Swift, Gay, and Arbuthnot in Historical Context; Liddell & Scott, Greek-English Lexicon, 9th Edition. Portraits of Jonathan Swift and John Arbuthnot, Wikimedia Commons. 

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