Small balances and large barrels
When building an Arnold & Son collection, all the thinking is focused on chronometry. The in-house manufactured calibres are based on advanced technical fundamentals that are not necessarily the best known. One is the choice of small, lightweight balances capable of rapidly returning to their isochronous rate after the latter has been disturbed by inevitable everyday shocks. Another is the routine use of large barrels or even two series-coupled barrels to store the energy required for the movement to function. They consequently provide Arnold & Son’s manual winding calibres with above-average power reserves of 90 hours and more. A third is the particular attention paid to manufacturing the gear trains, roller-burnishing the pinions and polishing the gear teeth, and the precision of the machining and therefore the relative positions of the moving parts, a key concept in rate accuracy.
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At the heart of chronometry
The tourbillon (or the fact of putting the regulating organ in rotation on its axis to best adjust the effects of gravity on the balance and its hairspring) was patented after John Arnold’s death. Still, it was undoubtedly at the heart of his chronometric research and discussions with his friend Abraham-Louis Breguet, who incidentally assembled his first tourbillon on a John Arnold regulator in homage to this great watchmaker. Nowadays, the tourbillon has become a must in Arnold & Son collections.
While the tourbillon was not a complication in John Arnold’s time, constant force underpinned the design of his marine chronometers. The regularity of the rate of the sprung balance relies on the consistency of the energy that it receives. However, this naturally fluctuates due to the circular and spiral nature of the mainspring contained in the barrel. To achieve a perfectly smooth torque, in other words a constant force, Arnold & Son uses a one-second constant-force mechanism. Housed just before the escapement, it stores up a small but always equal amount of energy in a secondary spring, the remontoire. Thus, every second, the sprung balance receives very precisely the same force to power its oscillations. These become more even, thereby creating the conditions for a high-precision rate.
True-beat seconds, a true complication
The Brand also works with another of John Arnold’s historical chronometry indicators: deadbeat seconds, a mechanism that was indispensable to navigators at the time for calculating longitude. This mechanism advances one step each second, rather than six or eight smaller jumps in sync with the balance frequency. Instead of the term deadbeat seconds, Arnold & Son prefers a name whose very sound means accuracy: “true beat second”. Its jump is a signature of John Arnold’s marine chronometers and a complication still alive and well in the collections.
Our collections in Angelus L.A.B.
