“... a piece of work which excites the admiration of the most learned mathematicians."
Cosmogrciphica Pomponii Melae (1511)
Often in history one critical invention leads to another that overshadows the first. This was true of the German locksmith Peter Henlein, the inventor of the portable or pocket watch. He created this sometime between 1504 and 1508, and it could operate for up to forty hours before it needed rewinding.
Henlein's work was made possible by the invention, more than fifty years earlier, of a single piece of metal that, when in a certain shape, would use the metal's natural elasticity to both absorb and release a force applied to it: the humble coiled spring. History does not recall who first created this most useful invention, but a small number of examples of spring-driven clocks have survived from the early fifteenth century.
The coiled spring's ability to store energy was what made it perfect to power clockwork devices. Winding up a clock, or watch, costs physical energy as the spring becomes compressed. Clockwork gears then allow that energy to be gradually released while supplying a steady, if tiny, flow of power to a clock.
Henlein, and others, had to overcome various problems in their early models. A good spring is created from a single ribbon of steel of uniform thickness that can be squeezed without breaking. The delicate preheating required to temper coiled springs was difficult, and perfecting the formula was an important step in metallurgy.
