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.
Sum of angles ofany triangle greater than 180 degrees. The following are actually delayed until the next class because this lecture will extend into the next period.