Fascinating. It’s crazy to think that with just the laws of gravity and some mathematical arranging, a series of pendulums could behave like this.
The longest pendulum pendulates 51 times every 60 seconds. Each progressively shorter pendulum is made just shorter enough to complete 1 additional pendulation, meaning that the 15th (i.e. final) pendulum pendulates 65 times in 60 seconds.
This specific pendulum design was created in 1867 by the mathematician Ernst Mach.
For further reading about this pendulum setup and its history see here.