**Note:**Do not rely on this information. It is very old.

# Cissoid

Cissoid, a curve of much interest in higher geometry. It may be drawn in the following manner: - A circle is described on a line A B as diameter; the tangent E B F is drawn touching the circle at B, and points C_{1}, C_{2} ..., on this tangent are joined up to A. Such lines all cut the circle at, say, D_{1}, D_{2} ..., and if on these lines AO_{1}, AO_{2} ...., are marked equal to C_{1} D_{1}, C_{2}, D_{2} . . , the points O_{1} O_{2}, ... will lie on the cissoid.