Griffiths' theorem

Griffiths' theorem: every red circle is a pedal circle of a blue point on the line through the circumcenter O, and G is the Griffiths point

Griffiths' theorem, named after John Griffiths (1837-1916), is a theorem in elementary geometry. It states that all the pedal circles for a points located on a line through the center of the triangle's circumcircle share a common (fixed) point. Such a point defined for a triangle and a line through its circumcenter is called a Griffiths point