Diagram, geometrical diagram by A [Amédée] Mannheim A geometrical figure, labelled figure 1, showing two perpendicular lines with various marked and dotted lines between them. Subject: Geometry / Trigonometry A print of this diagram was published in volume 33 of the Proceedings of the Royal Society alongside the paper 'Sur les centres de courbure principaux des surfaces homofocales du second ordre'. 1882