Vibration microscope, after Lissajous and Helmholtz

A violin string vibrates too fast to be visible for the human eye. By means of the ‘vibration microscope’, devised by the French physicist Jules Antoine Lissajous, Hermann von Helmholtz made one of the first attempts to understand what happens when a violin string is bowed by a violin bow. The apparatus is an elementary version of what is now called an ‘oscilloscope’. The objective of the microscope is mounted on one of the ends of an electrically driven tuning fork. Before this lens a violin string is stretched parallel to the tuning fork. If the string vibrates just as fast as the tuning fork, the string is seen as motionless. A small difference in oscillation period gives a slowly moving image. This was for Helmholtz the basis for a mathematical description of the string movement.