John Arnold - Patents and Plagiarism

Patents and Plagiarism

The fact that Arnold had greatly simplified the technology of the timekeeper with 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 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. 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 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.

Eventually, after much argument, the Board of Longitude granted Earnshaw and Arnold awards for their improvements to chronometers. Earnshaw received £2500 and John Arnold's son, John Roger Arnold, received £1672. 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 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. The facts prove that authors such as Gould and Sobel are incorrect in their assertion that there was commercial rivalry between Arnold Sr. and Earnshaw.