John Arnold was the first to design a watch that was both practical and accurate, and also brought the term “Chronometer” into 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 has remained, 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 wristwatches to this day.
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.
But three elements were necessary for 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