In 1880, Jaques and Pierre Curie discovered the piezoelectric properties that would later be used in quartz movements. More than four decades later, in 1921, Walter G. Cady built the first crystal oscillator. An oscillator is a circuit that uses mechanical resonance of a vibrating crystal of piezoelectric material to create an electric signal with constant frequency. Without the discovery of piezoelectric and the invention of the crystal oscillator, we would not have the timepieces we have today. The world's first quartz movement was invented in 1927 by Warren Marrison and J.W. Horton.