John Arnold was the first to design a watch that was both practical and accurate, and also brought the term "Chronometer" in to use in its modern sense, meaning a precision timekeeper. His technical advances enabled the quantity production of Marine Chronometers for use on board ships from around 1782. The basic design of these, with a few modifications unchanged until the late twentieth century. With regard to his legacy one can say that both he and Abraham-Louis Breguet largely invented the modern mechanical watch. Certainly one of his most important inventions, the Overcoil balance spring is still to be found in most mechanical wrist watches to this day.
It can be said that, from around 1770, Arnold continued the development of portable precision timekeepers almost from the point at which the development of John Harrison's precision timekeeper had ended. Compared to Harrison's watch, the basic design of Arnold's was very simple whilst being both consistently accurate and mechanically reliable. Importantly, the relatively conventional design of the movement facilitated its production in quantity at a reasonable price, also at the same time enabling easier maintenance.
Three elements were essential to this achievement:
- a detached escapement, which gave minimal interference with the vibrating balance and balance spring,
- a balance design that enabled compensation for the effect of temperature on the balance spring,
- a method for adjusting the balance spring, so that the balance oscillates in equal time periods even through different degrees of balance arc (isochronism).
Early life and work
John Arnold was apprenticed to his father, also a clockmaker, in Bodmin. He probably also worked with his uncle, a gunsmith. Around 1755, when he was 19, he left England and worked as a watchmaker in the Hague, Holland, returning to England around 1757.
In 1762, whilst at St Albans, Hertfordshire, he encountered William McGuire for whom he repaired a repeating watch. Arnold made a sufficient impression so that McGuire gave him a loan, enabling him to set up in business as a watchmaker at Devereux Court, Strand, London. In 1764, Arnold obtained permission to present to King George III an exceptionally small half quarter repeating watch cylinder escapement watch mounted in a ring. A similar repeating watch by Arnold has survived; it is of interest that the basic movement is Swiss in origin but finished in London. The escapement of this watch was later fitted with one of the first jewelled cylinders made of ruby.
Arnold made another watch for the King around 1768, which was a gold and enamel pair cased watch with a movement that had every refinement, including minute repetition and centre seconds motion. In addition, Arnold fitted bi-metallic temperature compensation, and not only was every pivot hole jewelled but the escapement also had a stone cylinder made of ruby or sapphire. This watch Arnold designated "Number 1" as he did with all watches he made that he regarded as significant, these numbering twenty in all.
Other early productions by Arnold from 1768 to 1770 display both originality and ingenuity; this includes a centre seconds watch wound up by depressing the pendant once a day. The movement of this watch also was fully jewelled with a temperature compensation device and a ruby stone cylinder escapement.
These watches were made as demonstrations of Arnold's talent, and, in terms of style and substance, were similar to other "conversation pieces" being made at the same time as those being produced for James Cox and made primarily for export to the East.
The technical challenge
Arnold's facility and ingenuity, coupled with his undoubted charm brought him to the attention of the Astronomer Royal Neville Maskelyne, who at this time was seeking a watchmaker skilled enough to make a copy of John Harrison's successful marine timekeeper. A full and detailed description of this watch was published by the Board of Longitude in 1767, entitled "The Principles of Mr. Harrison's Timekeeper", the intention clearly being for it to act as a blueprint for future quantity production. In fact it was a highly complex and technically very advanced piece of micro engineering, and capable of being reproduced by less than a handful of watchmakers. However, the challenge was taken up by Larcum Kendall ,who spent two years to make a copy (now known as "K1") that cost £450, a huge sum at the time. Although successful as a precision timekeeper, the Admiralty wanted a timekeeper on every major ship, and Kendall's was too expensive and took too long to make. Kendall made a simplified version (K2) in 1771, but this too was costly, and not as accurate as the original.
In retrospect therefore, it was a significant occasion when in 1767 Neville Maskelyne presented John Arnold with a newly printed copy of the "Principles of Mr. Harrison's Timekeeper", evidently with a view to encourage him to make a precision timekeeper of the same kind. Following this, Maskelyne encouraged Arnold by employing him on several occasions, mostly in connection with watch and clock jewelling. In 1769 Arnold modified Maskelyne's centre seconds watch by John Ellicott, changing the cylinder escapement from steel to one made of sapphire. This watch he lent to the Astronomer William Wales for use in assessing the practicability of Maskelyne's Lunar distance method for finding the ship's Longitude during the voyage of the Transit of Venus expedition to the West Indies in 1769. Around this time Arnold also seems to have started to think about making an accurate timekeeper to find the Longitude.
Arnold's first "Watch Machines"
Arnold's approach to precision timekeeping was completely different to that of Harrison whose technical ethos was rooted in seventeenth and early eighteenth century theory and practise. Arnold knew that as the balance and balance spring control the timekeeping in a portable watch, he only needed to find a way of giving the balance a consistent impulse with minimal interference from the wheel work, together with an effective temperature compensation. After making some experimental machines, he produced what could be regarded as a production model to the Board of Longitude in March 1771.
This machine was completely different to Harrison's watch. It was a mahogany box of approximately 6 x 6 x 3 inches that housed a movement that, though relatively simple, was close to the same size as Harrison's, with a balance of a similar diameter. The radical difference, however, was a newly designed escapement that featured a horizontally placed pivoted detent that allowed the balance to vibrate freely, except when impulsed by the escape wheel. The spiral balance spring also had a temperature compensation device similar to those in Arnold's watches, and based on Harrison's bimetallic strip of brass and steel. Arnold proposed manufacture of these timekeepers at 60 guineas each.
Three of these timekeepers traveled with the explorers James Cook and Captain Furneaux during their second voyage to the southern Pacific Ocean in 1772-1775. Captain Cook also had Kendall's first timekeeper on board as well as one of Arnold's. Whereas Kendall's performed very well and kept excellent time during the voyage, only one of Arnold's was still running on their return to England in 1775.
During this period, Arnold also made at least one precision pocket watch, a miniature version of the larger marine timekeepers.
This surviving watch watch dates from around 1769-1770, and is signed Arnold No. 1 Invenit et Fecit. The movement, which indicates centre seconds, has a steel balance with a bimetallic temperature compensation strip that acts on the flat balance spring. Though now altered, the original escapement was Arnold's horizontal pivoted detent as fitted to the larger timekeepers, which was it seems not entirely successful and needed improvements.
Around 1772, Arnold modified this escapement so that it now was pivoted vertically and acted on by a spring. This was a much more successful arrangement, and it is known that in 1772 at least two pocket timekeepers with this escapement were supplied to Joseph Banks at a cost of £100 and also Banks' fellow Etonian Captain Constantine John Phipps, 2nd Baron Mulgrave.
In 1773, Captain Phipps made a voyage to the North Pole taking with him not only his Arnold pocket timekeeper and an Arnold box timekeeper in gimbals, but also Kendall's "K2" timekeeper. From Phipps's account, it appears that the pocket watch performed very well indeed, and was a convenient instrument for ascertaining the longitude.
By 1772, Arnold had finalized the design of his pocket timekeepers and started series production with a standardized movement caliper, this being around 50 mm in diameter, larger than a conventional watch of the period, and showing seconds with a pivoted detent escapement and spiral compensation curb. However, the latter appears to have proved ineffective, which seems to have substantially slowed the rate of production.
Even though he produced a number of pocket timekeepers, from around 1772-1778, Arnold was still experimenting with different types of compensation balance and methods of balance spring adjustment. The most difficult problem to surmount was the problem of making an effective and continuously adjustable temperature compensation device. For technical reasons, the temperature compensation for the balance spring had somehow to be incorporated into the balance itself and not act on the balance spring directly as had been done previously by Arnold and others.
Arnold's first patent of 1775
In 1775, Arnold took out a patent for a new form of Compensation balance with a bimetallic spiral at the centre. This spiral actuated two weighted arms making them move in and out from the centre, changing the radius of gyration and thus the period of oscillation.
In the same patent, he included a new helical balance spring. This shape reduced lateral thrust on the balance pivots as they rotated, and reduced random errors from the "point of attachment" effect, which any balance with a flat spring suffers from. As Arnold stated rather succinctly in a 1782 letter to the Board of Longitude, "...the power in all parts of the spring is uniform."
The fact that Arnold had recognized the technical advantages of a balance spring of this form clearly demonstrates a high degree of insight. The balance that was the subject of the patent appears to have been an unsuccessful design. Certainly some marine chronometers used this balance, but none have survived. Pearson records a balance of this kind in his possession that was 2.4 inches in diameter.
From 1772 to 1775, Arnold also made about thirty five pocket timekeepers. Not many, about ten of these, survive and none in their original form, as Arnold was constantly upgrading their specification. They appear originally to have had a pivoted detent escapement, with a steel balance and a helical balance spring. A spiral bimetallic curb acting on this spring was intended to provide the temperature compensation, but this system evidently did not work, as every watch was subsequently altered and improved by Arnold shortly afterwards. Surviving chronometers from this series include Numbers 3,29 and 28.
Further experimentation and invention by Arnold led to a breakthrough in the late 1770s. He redesigned the compensation balance and developed two designs that showed promise. Known as the "T" and "S" balances, and marked as such in Arnold's 1782 patent (probably because of their appearance), both employed bimetallic strips of brass and steel with weights attached, which changed the radius of gyration with change in temperature. Although these probably needed a lot of adjustment, they appear to have worked well compared to his previous attempts at a compensation balance.
A revolution in precision timekeeping
Around 1777 Arnold redesigned his chronometer to make it larger, probably to accommodate the new balance that worked with his pivoted detent escapement and patented helical spring. The first chronometer of this pattern was signed "Invenit et Fecit" and given the fractional number 1 over 36, as it was the first of this new design.
It is generally known as "Arnold 36" and was in fact the first watch that Arnold called a "Chronometer", a term which subsequently came into general use and still to this day refers to any highly accurate watch.
The performance of this chronometer exceeded all expectations and proved to be extremely accurate when tested for thirteen months at the Royal Observatory, Greenwich from February 1, 1779 to July 6, 1780. All the more remarkable is the fact that not only was it placed in several positions during the trial but even worn at some point and carried around.
During this period the timekeeping error was 2 minutes 32.2 seconds, but the error in the last nine months amounted to just one minute. The greatest error in any 24 hours was only four seconds, or one mile of Longitude.
Subsequently Arnold produced a pamphlet detailing the trial and the results with attestations of veracity from all those concerned with testing it, in charge of this was Maskelyne's assistant the Rev. John Hellins. The astonishing performance of this watch caused controversy because many thought the result either a fluke or a fix of some kind, particularly as Maskelyne was effectively one of Arnold's patrons.
However, from the technical point of view the design was entirely sound and therefore proved highly accurate over long periods. Arnold evidently learned the lessons that Harrison had learned before him, By using a large, quickly oscillating balance (18,000 beats per hour) with small pivots. Arnold's detent escapement provided minimal interference with the controlling helical balance spring, since the temperature compensation was in the balance itself. this was suggested by Harrison as being a prerequisite, although he never developed this idea. An important point concerning Arnold's pivoted detent escapement is that it did not need oil on the acting surfaces, with the advantage that the rate of going did not deteriorate and remained stable for long periods. At the time, the only oil available was vegetable in origin and degraded fairly quickly compared to modern lubricants.
This chronometer 60mm in diameter is housed in a gold case, and miraculously has survived in a perfect and original condition. It can be seen in the collections of the National Maritime Museum, Greenwich, London, having been saved for the nation in 1993.
In Britain prior to Harrison's marine watch, it seems to have been generally thought that a small or very small watch (Such as Arnold's ring watch) was the ultimate test of watch making skill especially with regard to complex watches and those built for accuracy. But both Harrison and Arnold had demonstrated that an accurate watch had to be of large diameter. So, by the end of the eighteenth Century, a large diameter watch was regarded as characteristic of a superior watch.
Arnold's second patent of 1782
In 1782, Arnold took out another patent; he did this to protect the latest and most important inventions, which were potentially lucrative. Several other watch makers most notably Thomas Earnshaw had started to copy Arnold's work, the latter around 1780 modifying his detent escapement by mounting the detent on a spring and creating the spring detent escapement.
During the same period between 1779 and 1782, Arnold had finalized the form of his chronometer watches. As a result of continuous experimentation, he had worked out a way of making an effective but simple form of compensation balance and, at the same time, discovered a simple modification to his helical balance spring, which enabled it to develop concentrically and in addition conferred the property of isochronism on the oscillating balance. Not only this, but for adjustments to both the compensation balance and the balance spring could be carried out in a simple but calculated way. These were the main subjects of the patent, which he took out in 1782.
Concerning the balance, this consisted of a circular steel balance wheel to which two bimetallic strips were attached diametrically. Each bimetallic strip terminated with a screw thread on which was mounted a weight or balance nut. The further along the strip this nut was screwed, the greater the compensating effect. Another part of the patent concerned an addition to the form of the balance spring, this being a coil of smaller radius being made at each end of the helical spring, which offered an increasing amount of resistance to the rotating balance as it turned towards the end of each vibration. This was an important invention as it largely eliminated the problem of the positional adjustment of balance controlled watches. This device known as the "Overcoil Balance Spring" is still used today in most precision mechanical watches.
Another part of the patent concerned the escapement, this was a modification of Arnold's pivoted detent escapement which essentially mounted the detent on a spring. The specification only shows the part of this escapement, which is the method of impulse on the impulse 'roller'.
Patents and plagiarism
The fact that Arnold had greatly simplified the technology of the timekeeper with simple yet effective mechanical techniques also meant that these methods could be easily copied and utilised by other watch makers without permission, this is why Arnold took out his patents.
There were two other makers also made precision watches with the detached escapement, both were friends of Arnold and both employed the highly skilled workman and escapement maker Thomas Earnshaw. Emery used with Arnold's permission an earlier form of his compensation balance and helical balance spring, in conjunction with the detached lever escapement of Thomas Mudge, and John Brockbank employed Earnshaw to make his pattern of chronometer but with Brockbank's design of compensation balance.
In 1780, while making these chronometers for Brockbank, Earnshaw modified the pivoted detent by mounting the locking piece on a spring thus dispensing with the pivots. He regarded this as a great invention, although, in fact, it was only a minor improvement. Arnold managed to see this new idea and promptly took out the 1782 patent for his own design of spring detent, but it is not known whether this preceded Earnshaw's own idea.
Therefore, there has been a great deal of debate over who was the inventor of the spring detent escapement, Arnold or Earnshaw. This argument, first initiated by Earnshaw has been continued by horological historians such as Rupert Gould even up to the present, none recognizing the fact that it was not any particular form of detached escapement, which led to Arnold's success but was due to his methods of adjusting the balance spring for positional errors. Arnold probably tried to keep these secret, it is recorded that he clearly expressed his concerns about possible plagiarism to Earnshaw, warning him not to use this particular form of balance spring.
Nevertheless, Earnshaw through another watchmaker Thomas Wright, took out a patent a year later in 1783, and included in the multiple specification was Earnshaw's pattern of integral compensation balance and spring detent escapement. However both of these were practically undeveloped and the balance especially had to be redesigned.
But importantly, because Arnold's balance spring patents were in force (each for 14 years) Earnshaw could not use the helical balance spring until the 1775 patent lapsed in 1789 and in the case of the 1782 patent, 1796. It is evident that until around 1796 Earnshaw made watches with flat balance springs only, but post 1800 practically every marine chronometer including those by Earnshaw had a helical spring with terminal overcoils.
Significantly, it is from this date that Earnshaw and others started to have any kind of success in producing successful marine and pocket chronometers. Early examples by Earnshaw even copy Arnold's style of engraved signature which includes the legend "Invenit Et Fecit" as well as a fractional number.
Arnold was the first to produce marine and pocket chronometers in significant quantities at his factory at Well Hall Eltham from around 1783, during the next 14 or 15 years he produced hundreds before he had any kind of commercial competition at all. The facts prove that authors such as Gould and Sobel to be quite incorrect in their assertion that there was commercial rivalry between Arnold Sr. and Earnshaw.
Arnold and Breguet
The important French watchmaker Abraham-Louis Breguet was a great friend of Arnold, who it seems gave him permission carte blanche to incorporate or develop any of Arnold's inventions and techniques into his own watches. These included his balance designs, helical springs made of steel or gold, the spring detent escapement, the overcoil balance spring and even the layout of an Arnold dial design which Breguet incorporated into his own. These were made from engine-turned gold or silver, this pattern becoming the classic and distinctive "Breguet dial", which in terms of design are identical in layout to the enamel dials which Arnold had designed for his small chronometers, these first appeared in 1783.
Arnold also appears to have been the first to think of the concept of the Tourbillon, this probably derived from his known work on the recognition and elimination of positional errors. In the Tourbillon device, the balance and escapement is continuously rotated and virtually eliminates errors which stem from the balance not being perfectly balanced. Arnold seems to have experimented with this idea but died in 1799 before he could develop it further. It is known that Breguet made a successful and practical Tourbillon mechanism around 1795, but nevertheless he acknowledged Arnold as the inventor by presenting his first Tourbillon in 1808 to Arnold's son John Roger. As a tribute to his friend Arnold Sr. he incorporated his first tourbillon mechanism into one of Arnold's early pocket chronometers, Arnold No.11, this has an engraved commemorative inscription dedicating his gift to the revered memory of Arnold. This significant watch can be seen today in the British Museum's collection of clocks and watches.
By the time of Arnold's death in 1799 he was the most famous watch maker in the world, and his pre - eminence as the inventor of the precision chronometer was recognized by all.
John Roger Arnold
Arnold's son John Roger Arnold was born in 1769 and served an apprenticeship with both his father and the eminent French watchmaker Abraham Louis Breguet. He became Master of the Worshipful Company of Clockmakers in 1817. From 1787 he and his father founded the company Arnold & Son. After his father's death in 1799, John Roger continued the business, taking into partnership John Dent between 1830 and 1840. After his death in 1843 the company was bought by Charles Frodsham.
The brand name Arnold & Son used by a Swiss watch company has absolutely no connection to the original firm founded by John Arnold.
Pocket watch by Arnold and Dent hallmarked 1835
