Early theories of how light was transmitted were briefly discussed, these included corpuscular theory and streamer theory. The more modern dual theory was touched on, with light acting at times like a particle and at other times like a wave. A demonstration was used to show that an electric field produced a magnetic field, and that a magnetic field produced an electric field. Light was defined as an electro-magnetic wave, one in which each field generated the other, which propelled the wave, without a medium needed. A sketch of an electro-magnetic wave showed both phases and direction of motion.