Why pendulum clocks swing together found

Scientists may have finally solved a 350-year-old mystery of why pendulum clocks hanging from the same wall synchronise over time.
Almost 350 years ago, Dutch physicist Christiaan Huygens, inventor of the pendulum clock, noticed that no matter how the pendulums on two clocks hanging on the same wall began, within about a half-hour, they ended up swinging in exactly the opposite direction from each other.
The cause of this effect - what Huygens described an "odd kind of sympathy" - remained a mystery for centuries.
However, recently scientists analysing two pendulum clocks hanging from the same beam found that the clocks could influence each other through small forces exerted on the supporting beam, 'Live Science' reported.

Henrique Oliveira and study co-author Luis Melo, both from the University of Lisbon in Portugal, decided to analyse how two pendulums might interact through an immobile wall.
The researchers calculated that, as pendulums move back and forth, sound pulses could travel through the wall from clock to clock.

These pulses can interfere with the swings of the pendulums, eventually causing them to synchronise.
Researchers tested their idea with experiments involving two pendulum clocks attached to an aluminium rail fixed to a wall.
Their results showed that changes in the speed of the pendulum swings coincided with cycles of those sound pulses.