Where did Benjamin Franklin do his science? The famous American Founder is closely associated with his political career, meaning his public life. Compared to that public life, Franklin's science has seemed to be an odd, private hobby, which he managed to do somehow (and somewhere) alongside his work in politics. But Franklin's scientific and political efforts were interconnected. In fact, he performed much of his science in public places. To be sure, he did some of his scientific investigations in private, at home. (He used his house as an experimental space for his work on heat and rigged up the house itself as a piece of electrical apparatus.) But in Franklin's Philadelphia, the best space for science was a public one: the Pennsylvania State House, now Independence Hall. Franklin had helped to found a learned society, the Library Company of Philadelphia, which for some time used rooms in the State House's west wing. There, the company had hosted a series of scientific lectures, including demonstrations with an air pump, which created an experimental vacuum; there, as well, Franklin and his collaborators did most of their famous electrical experiments. The open area outside the State House proved useful for astronomical observations and for the launch of the first balloon in the United States. The public space for science also functioned as a place for politics. A platform built for observations of the 1769 Transit of Venus was the very spot on which, seven years later, the Declaration of Independence had its first public reading. This lecture will explain why Franklin and his contemporaries expected their science to fit comfortably into public life--and public space. What kind of science was it?