September 14th is Charles François de Cisternay du Fay's birthday. He was French scientist who discovered there were two types of electrical charge: vitreous and resinous. We know them as positive and negative today. He named his charges after the methods he used to generate the charge. Vitreous (Latin for glass) electricity is generated when glass is rubbed with fur. Resinous (Latin for resin or amber) electricity is obtained from rubbing amber with silk or paper. He also noticed the different charges would attract each other, but the same kind of charge would repel each other. He developed a theory to explain this behavior where there existed two different fluids. Neutrally charged objects would have equal amounts of both fluids which would neutralize each other. When rubbed, an object would lose one of these fluids and leave an excess of the other. Today, we know the transfer of electrons is involved in this behavior, but it helped usher in a new study in science. Find out what else occurred on this day in science history.