Robert Hooke (1635-1703), Joseph Knibb (1640-1711) When we think of the people who design and build clocks, we tend to think of them as clock makers. But if you think about it, a clock maker is a mechanical engineer. working with springs, gears, and mechanical oscillators to create a timekeeping device. The pendulum clock was one of the first timekeeping devices to work with reasonable accuracy. These clocks ranged in size from small boxes to giant towers, the precursors to structures like Big Ben. The key innovation was the anchor escapement mechanism, developed by Robert Hooke around 1657 and perfected by clockmaker Joseph Knibb in 1670. This was the linchpin in a system to convert the motion of a mechanical oscillator into the movements of the clock's hands. The oscillator could be a swinging pendulum typically seen in a wall clock or grandfather clock) or a wheel that rotates back and forth (typically seen in a watch). The engineer needs to accomplish two things with the pendulum. First, enough energy - in the form of a little push during each swing — needs to be added to overcome the pendulum's loss of energy to things like air resistance. This keeps the pendulum swinging indefinitel. Second, each pendulum stroke must convert to the correct angular movement of the second hand. The mechanism that accomplishes these two things is called an escapement, and it works in conjunction with a spring or a falling weight to obtain the energy to push the pendulum and move the second hand. Having arranged a pendulum, a source of energy, an escapement, and a second hand, the the rest of the clock is just appropriate down-gearing to spin the minute and hour hands at their cousect rates. A mechanical clock is born. Ever mechanical clock you have ever seen is simply an engineers creative rendering of the four fundamental parts- oscilator energy soutce, escapesnent, and gearing - to get the clock's hands to move properly.