Lemniscate of Bernoulli

I am afraid that your browser cannot handle Java code. 
Equation: r2 = a2cos(2 theta)

Use the buttons on the right to move the graph or the ones in the middle to alter the scale. The buttons on the left can be used to alter the value of the parameter a. The two "inc" buttons alter the rate at which you can vary the parameter. 

You can see the Java source code.

BS/JOC/EFR July 1996

All credit for this applet goes to the guys at  http://www-history.mcs.st-and.ac.uk/~history/Java/ .