John Arnold (1736 – 1799) was born in Cornwall and was apprenticed to his father, also a clockmaker. He probably also worked with his uncle, a gunsmith. Around 1755, he left England and worked as a watchmaker in the Hague, the Netherlands, returning to England around 1757.
In 1762 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. In 1764, Arnold obtained permission to present to King George III an exceptionally small half quarter repeating watch with cylinder escapement mounted in a ring. A similar repeating watch by Arnold has survived; it is of interest that the basic movement is of 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. 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 1765 to 1770 display both originality and ingenuity; this includes a centre seconds watch (later re-cased, dial replaced) wound up by depressing the pendant once a day. The movement of this watch also was fully jewelled (around 25) with a temperature compensation and originally had a ruby cylinder escapement (B). The watch is also numbered ‘1’ and its main spring is scratch-dated 1766 (B). It represents the earliest known movement with jewelled cylinder (later replaced) and the first known keyless movement (B).
Arnold’s facility and ingenuity 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. However, the challenge was taken up by Larcum Kendall, who spent two years making a near identical copy (K1) that cost £450, a huge sum at the time. Although successful as a precision timekeeper, the Admiralty for obvious reasons 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, leaving out the complicated remontoir system. But the result was still too 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 copy of the ‘Principles of Mr. Harrison’s Timekeeper’ as soon as it was published, evidently with a view to encourage him to make a precision timekeeper of the same kind.
It was from around 1770 that Arnold developed the portable precision timekeeper, almost from the point where John Harrison ended his work in this field. But compared to Harrison’s complicated and expensive watch, Arnold’s basic design was simple whilst consistently accurate and mechanically reliable. Importantly, the relatively simple and conventional design of his movement facilitated its production in quantity at a reasonable price whilst also enabling easier maintenance and adjustment.
Three elements were necessary for this achievement:
• Escapement: A detached escapement: minimal interference with the vibrating balance and balance spring
• Balance: A balance design that enabled compensation for the effect of temperature on the balance spring
• 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
After making some experimental pieces, he produced what could be regarded as a production model to the Board of Longitude in March 1771. This piece was completely different from Harrison’s watch. It was relatively simple, 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 (detached escapement). The spiral balance spring also had a temperature compensation device similar to 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 Captain James Cook and Captain Furneaux during their second voyage to the southern Pacific in 1772 – 1775. Captain Cook also had Kendall’s first timekeeper on board as well as two 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.
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.
In 1773, Captain Constantine 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.
It seems likely that before 1775 Arnold’s earliest pocket chronometers were plain watches with centre seconds.
By 1772, Arnold had finalised the design of his pocket timekeepers and started series production with a standardised movement caliber, 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.
In 1775, Arnold took out a patent for a new form of compensation balance with bimetallic inserts. These inserts 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 recognised the technical advantages of a balance spring of this form clearly demonstrates a high degree of insight. 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. Surviving chronometers from this series include Numbers 3, 28 and 29.
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 ‘double T’ and ‘double S’ balances, and marked as such in Arnold’s 1782 patent, 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.
Around 1777 Arnold redesigned his chronometer, making it larger in order to accommodate the new ’T’ 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 that subsequently came into general use and still means any highly accurate watch. The Royal Observatory in Greenwich tested ‘Arnold 36’ for thirteen months. The testers placed it in several positions during the trial, and even wore it and carried it around. The watch exceeded all expectations, as it demonstrated great accuracy. 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 nautical mile of Longitude at the equator.
Subsequently, Arnold produced a pamphlet that detailed the trial and results, with attestations of veracity from all those concerned with the tests. The astonishing performance of this watch caused controversy, because many thought the result was either a fluke or a ‘fix’ of some kind, particularly as Maskelyne was, effectively, one of Arnold’s patrons.
From a technical point of view, however, the design was entirely sound and highly accurate over long periods. Arnold evidently understood and applied the lessons that Harrison had learned before him—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. Harrison had suggested this as a prerequisite, though he never developed the idea. Arnold’s pivoted detent escapement did not need oil on acting surfaces, with the advantage that the rate of action did not deteriorate, and remained stable for long periods. At the time, only vegetable oil was available, which degraded quickly compared to modern (mineral) lubricants.
This chronometer, 60mm in diameter, is housed in a gold case, and miraculously has survived in perfect and original condition.
Both Harrison and Arnold demonstrated that an accurate watch had to be of large diameter, so by the end of the 18th century, a watch of large size was considered the primary characteristic of a well made and superior watch.
The fact that Arnold had gained great success by modifying the technology of the timekeeper by means of simple yet effective mechanical techniques, also meant that other watchmakers could copy these methods and use them without permission. This is why Arnold took out his patents.
Two other makers also made precision watches using detached escapements: Josiah Emery and John Brockbank. Both were friends of Arnold, and both employed the highly skilled workman and then escapement maker Thomas Earnshaw. Josiah 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. Earnshaw stated that Arnold managed to see this new idea and promptly took out the 1782 patent for his own design of spring detent.
Therefore, there has been a great deal of debate over who invented the spring detent escapement, Arnold or Earnshaw. This argument, first initiated by Earnshaw has been continued by horological historians such as Rupert Gould to the present. However the argument is irrelevant. In recent years, research has established that Arnold’s success was not due to the form of detent escapement, but to his original methods of adjusting the balance spring for positional errors by manipulating the overcoil terminal curve. For obvious reasons Arnold tried to keep these methods secret, certainly it is recorded that he clearly expressed his concerns about possible plagiarism to Earnshaw, warning him in no uncertain terms not to use his helical balance spring.
Nevertheless, a year later, in 1783, Earnshaw—through another watchmaker, Thomas Wright—took out a patent that included Earnshaw’s pattern of integral compensation balance and spring detent escapement in the multiple specification. However both of these were undeveloped and compared to Arnold’s were of little use, the balance especially having to be redesigned.
The bimetallic compensation balance and the spring detent escapement in the forms designed by Earnshaw have been used essentially universally in marine chronometers since then, and for this reason Earnshaw is also generally regarded as one of the pioneers of chronometer development.
However, 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. 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.
Arnold was the first to produce marine and pocket chronometers in significant quantities from around 1783, during the next 14 or 15 years he produced hundreds before he had any kind of commercial competition. The facts prove that authors such as Gould and Sobel are quite incorrect in their assertion that there was commercial rivalry between Arnold Sr. and Earnshaw.
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 he, Jean – Antoine Lépine and Abraham – Louis Breguet largely invented the modern mechanical watch. Certainly one of Arnold’s most important inventions, the overcoil balance spring is still to be found in most mechanical wrist watches to this day.
Arnold and Breguet
The French watchmaker Abraham – Louis Breguet became a great friend of Arnold. In 1792 the Duke of Orleans met Arnold in London and showed him one of Breguet’s clocks, and Arnold was so impressed that he immediately travelled to Paris and sought permission for Breguet to take on his son as his apprentice. Arnold appears to have given Breguet ‘carte blanche’ to incorporate or develop any of Arnold’s inventions and techniques into his own watches (see Breguet No. 165 and No. 178).
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 that Breguet incorporated into his own. These were made from engine-turned gold or silver—a pattern that became the classic and distinctive Breguet dial. Arnold’s pattern first appeared in 1783 on the enamel dials Arnold designed for his small chronometers, and the proportions and layout of their figuring is identical to that of the classic ‘Breguet’ type of engine turned metal dials which appeared around 1800, and which were quite unlike anything else made in France or Switzerland at the time.
Arnold also appears to have been the first to think of the concept of the ‘tourbillon’, this must have derived from his known work on the recognition and elimination of positional errors. In the tourbillon system, the balance and escapement is continuously rotated and virtually eliminates errors arising from the balance wheel not being perfectly balanced whilst in vertical positions. Arnold appears 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 by presenting one of his first (certainly not the first) tourbillon in 1808 to Arnold’s son John Roger. It is a tribute to his friend Arnold Sr. and he incorporated his tourbillon mechanism into one of Arnold’s early pocket chronometers, Arnold No.11. An engraved commemorative inscription on this watch reads:
“The first tourbillon timekeeper by Breguet incorporated into one of the first works of Arnold. Breguet’s homage to the revered memory of Arnold, given to his son AD 1808.”
John Arnold’s pocket chronometer numbering system
Arnold’s pocket chronometers can be differentiated into several categories. The largest versions are the ‘best kind’ The numbering starts with No. 75. In 1794, this version changes. The slot for the detent is placed in line with the maintaining power detent arbor as in the ‘second kind’ versions. This new version retains the larger size. The numbering is given with a fraction or without.
The ‘second kind’ watches are smaller and their new numbering is given in fractions which difference is 301. Vaudrey Mercer believes that the difference states the total number of pocket timekeepers made until starting this new series. This kind has a new layout and is the escape wheel is smaller and positioned better. The first watch of this type is numbered 1/302 and was made 1783. These watches have the Arnold spring detent and a balance of the OZ type. When including John Roger into the firm in 1787, the numbering reaches 126/427, the last number recorded is 518/819 made in 1796.
The ‘second best kind’ are big and similar to the best kind but they lack the seconds dial. The fraction numbering differs by 1000, only three watches of this kind are known.
Antiquarian Horology 
