Nineteenth-century master horologists worked extensively on detached escapements for clocks. The most highly perfected mechanisms were destined for observatories, where they set the standard for timekeeping accuracy, or were used by régleurs at the many manufacturing companies, where the need for instruments with which to control their work was becoming more and more pressing. A multitude of devices saw daylight, many of which achieved extraordinary levels of precision. The majority of precision clocks were fitted with a “Graham” or “Lepaute” escapement, although a not insignificant number were equipped with more exotic systems, even prototypes.
Naming every maker to have produced an example of this type of regulator would be an impossible task, and so we shall limit ourselves to deadbeat or verge escapements, such as those by Bethune and Galileo, John Harrison’s grasshopper escapement for the H1, detached or lever escapements, such as those by Graham and Lepaute which formed the backbone of nineteenth-century systems, and the rarer “gravity” escapements, such as the one built by Thomas Mudge in 1795. This latter category bears a strong resemblance to detent escapements (and even that of Berthoud) in that friction is reduced to a strict minimum. Almost all these highly precise and lightweight mechanisms – to which we can add those of Denison, Thwaites & Reed or Reed alone, on display at the Musée de l’Horlogerie in Cluses, France, and at the Musée International d’Horlogerie in La Chaux-de-Fonds, Switzerland, not forgetting others by Bloxham, Ernest A. Hummel, Cole (1880), Arnfield or Seth Thomas – were reserved for precision instruments, observatory regulator clocks and, occasionally, tower clocks.
With the advent of electricity, all these wonderful escapements were progressively sidelined in favour of mechanisms which, responding to magnetic forces, kept the pendulum swinging by impulses without any contact; an advantage in terms of precision. If kept under a dome, in a vacuum, these clocks could reach a degree of precision almost equal to that of the very best quartz clocks. Except that as quartz technology spread, electric clocks were slowly relegated to history; as would be the quartz rod master clocks, replaced by the first atomic clocks whose almost perfect precision defies belief.
The major watch Manufactures that emerged in the mid-nineteenth century demanded efficiency, including from the escapements they used. Thomas Mudge’s mechanism, known to us as the Swiss lever escapement, was by far the most suited to these early days of industrialisation. At the same time, some of the smaller manufacturers – the “farmer-watchmakers” working in the countryside of the Jura and Faucigny regions – continued to make cylinder escapements right up until the eve of the First World War. For the vast majority of production, however, the Swiss lever escapement became the norm.
Thomas Mudge's escapement, known to us as the Swiss lever escapement, proved best suited to the early days of industrialisation.
The club-toothed escape wheel, in steel, engages with the lever, also in steel or in nickel with ruby pallets (until 1905, after which the Verneuil process was sufficiently developed to replace them with synthetic sapphires). They were coupled with a balance, generally a bimetallic (brass and steel) split-rim balance with a compensation screw, fitted with a blued steel balance spring with a Breguet or flat terminal curve. Certain executions differed from the prescribed construction; some, for example, used a straight line lever, with or without compensation, and more or less exotic escape wheels. Generally speaking though, all these mechanisms came under the label of detached escapement.
A turning-point in the 1930s
As cylinder escapements were phased out between the two world wars, an alternative had to be found that would be both robust and cheap enough for industrial production. The pin-pallet escapement ticked all the boxes. Already used for inexpensive table clocks and alarm clocks for the low end of the market, this type of construction found its way into “dollar” watches too. The American firm Ingersoll made widespread use of pin levers, as did Swiss maker Oris which didn’t make the transition to jewels until the 1960s. The only improvements made to escapements during this time were the development of quality alloys for the balance spring, of a shock-absorber system – the “pare-chute” which Abraham-Louis Breguet invented to protect his fragile ruby cylinder escapements (see How we put the spring into watches (I)) – and monometallic balance wheels, machined from a beryllium bronze strip. Some particularly inspired inventors set out to improve this mechanism by incorporating it into a system that would even out the power transferred to the balance wheel, resulting in (for instance) the constant-force Swiss lever escapement, an example of which can be seen in the A. Lange & Söhne Lange 31. When torque from the mainspring is high – in the case of the Lange, sufficient to provide 31 days of power reserve – it delivers a uniform amount to the regulator.
These concepts, specially adapted for watches competing in timing trials, were feats of miniaturisation and, as such, rarities. Towards the late 1930s, the chronos and other timers that were mounted on the instrument panels of cars and cockpits demanded reliable, long-lasting lubrication, and so the first attempts were made to improve oiling in escapements. Refined neatsfoot oil was replaced by low-evaporation synthetic ethers. Similarly, parts were coated with epilame to reduce surface tension and prevent oils from running off. These could be synthetic paraffin for high-efficiency escapements, or a conventional glycol ether such as Moebius oils.