Ever since the invention of the earliest water clocks, physics and gravity have affected our efforts to measure time precisely. Liquid-filled clocks ran faster when full, because higher pressure at the bottom of the vessel caused the water to drain more quickly. Springs provided a technological step forward, but not a complete solution, because they produce more force at full wind and less as they wind down. The balance wheel and balance spring represented another advance, yet gravity affects their precision as they change position. Brilliant clock and watchmakers have designed ingenious solutions for these problems, and Arnold & Son combines three of them, including its own patented mechanism, in the new Constant Force Tourbillion.
The first problem arises from the fact that a fully wound mainspring produces far more force than one at a low state of wind. That affects how much energy flows through the gear train and reaches the escapement. If the balance wheel at first receives very strong impulses, then later very weak ones, the length of time it takes to complete its swings will vary, making the timekeeping inconsistent.
Arnold attacks the non-linear energy release twice. At the source of the power, Arnold provides a unique mainspring barrel arrangement. Two symmetrical barrels in series operate in a complementary fashion. The first barrel powers the gear train by itself, and the second barrel springs into action (sorry) whenever the first barrel’s torque output drops below the optimal level. This system produces a smoother flow of energy to the escapement and the balance wheel, compared with a single-barrel movement.
At the other end, the movement contains a patented constant force mechanism. Power from the mainspring barrel charges a small hairspring which in turn releases a consistent amount of power to the escapement once each second. The patented constant force device rotates once per minute in increments of one second, mirroring the tourbillon cage. As you might guess, this system causes the seconds hand to jump forward once each second. In a happy coincidence, this so-called jumping or dead seconds (better known to Arnold fans as true-beat seconds) is a complication closely associated with Arnold & Son.
Finally, having doubly banished the evils of the non-linear torque curve, a one-minute tourbillion averages out gravitational errors by constantly rotating the escapement through 360 degrees of motion. When the power output from both barrels falls below the minimum acceptable level, the movement stops, rather than running at a sub-optimal rate.
This impressive collection of technical prowess is known as Caliber A&S5119. It’s a hand-wound manufacture movement running in 39 jewels at 21,600 vph for 90 hours. The movement features hand-chamfered bridges with polished edges, screwed gold chatons, and screws with beveled and mirror-polished heads. The tourbillion cage is also hand-chamfered and mirror-polished. The movement is set in an 18k red gold case measuring 46mm in diameter. A sapphire display back allows an unobstructed view.
The Arnold & Son Constant Force Tourbillon will be produced in a limited edition of 28 pieces, priced at $197,500. Complete specifications appear below.