Unpublished diagram, 'Diagrammatic representation of the apparatus employed in the experiments' by Edmund Johnson Spitta A plan of the equipment used in Spitta's experiments on the sine law of Malus. A lamp shines through a slit attached to a collimator, directed towards a double image prism in front of a screen. Behind the prism are a photometer, a large Nicol's prism, a corrected lens in front of a small diaphragm, two prismatic glasses and a wooden support 'carrying the paper screen for the projection of the images.' Subject: Optics / Scientific apparatus and equipment 1889