[Illustration]
Take two panes of common window-glass, about six inches square, set them
together at one side, and at the other side prevent them exactly joining
by a little wax, so that the two planes form a very small angle, as one
or two degrees. Then place the bottom edge about an inch down into a
dish of water, when the water will rise between the panes in the form of
a hyperbola.
[Illustration]