Even a simple harmonograph as described can create ellipses, spirals, figure eights and other Lissajous figures. By varying the frequency and phase of the pendulums relative to one another, different patterns are created. One pendulum moves the pen back and forth along one axis and the other pendulum moves the drawing surface back and forth along a perpendicular axis. Ī simple, so-called 'lateral' harmonograph uses two pendulums to control the movement of a pen relative to a drawing surface. The devices, which began to appear in the mid-19th century and peaked in popularity in the 1890s, cannot be conclusively attributed to a single person, although Hugh Blackburn, a professor of mathematics at the University of Glasgow, is commonly believed to be the official inventor.

The drawings created typically are Lissajous curves, or related drawings of greater complexity. You can try to put a diode in series with the coil and use it to charge up a capacitor with a high impedance digital multimeter you may be able to see the voltage build up.A harmonograph is a mechanical apparatus that employs pendulums to create a geometric image.

The experiment that you can now do is to see how long it takes the pendulum to be damped depending on the size of the resistor: this will give evidence that energy is extracted from the motion (if you do this with a free swinging pendulum the math is probably easier). Now close the circuit - with a short circuit, or with a resistor of different sizes. Initially, leave the wires open (no closed circuit) and set the pendulum ticking. Tape the coil to a piece of cardboard, and put it behind the pendulum - close, but not touching. Make a coil of magnet wire with about 100 turns and the same diameter as the magnet (or a little bit bigger, but smaller than the amplitude of the pendulum swing). Tape a strong disk magnet to the back of the pendulum. This is of course a function of the amount of energy you try to extract. If you have a good pendulum clock, you may be able to extract a minute amount of energy from it - but usually any additional friction will cause the clock to stop ticking.

Three pendulum rotary harmonograph math