Answer question posed in class. Newton believed light was particles that were separated by the prism. Students can move side to side and hear interference. To illustrate that light shows the same type of interference as sound.
Light is a wave.
This is where things stood in 1880 after Maxwell. To have discussion on importance of scientists and others - Good discussion in class. Shows light crossing a train perpendicular to the motion, as seen by obervers on train and on te ground. Shortest lines is geodesic, not a straight line. Lines return to themselves.