Griffiths' Theorem

When a point $P$ moves along a line through the Circumcenter of a given Triangle $\Delta$, the Circumcircle of the Pedal Triangle of $P$ with respect to $\Delta$ passes through a fixed point (the Griffiths Point) on the Nine-Point Circle of $\Delta$.

See also Circumcenter, Griffiths Points, Nine-Point Circle, Pedal Triangle