In Washington, of course, I continued what I like to do. Many particular papers; I might mention only one because it became rather practical - the BET paper, Brunauer, Emmet, Teller - discussing the very simple problem of absorption of whatever, molecules, on a plain surface. That was well understood in the case of a single layer absorption. But my friends in Washington had worked on absorptions where obviously many layers were absorbed and had fantasies about molecular forces that reached out over many layers. And I knew that such a thing was nonsense. And I've told my friends, Brunauer and Emmet, that it is nonsense. And my- their answer was- Well, here are our facts and we will consider that as a proof of distant forces, unless you can offer us something better. So under compulsion I said- Very simple, we have a monolayer absorption and that layer then acts as the new surface to absorb the next layer and that absorbs the next layer. And therefore, once you have ten layers you are almost as good as having a liquid on which you condense one more layer. And your polylayer absorption must therefore have a lot in common with the formation of liquids. That was the origin of the BET Theory which has one very particular property. Because it connects the absorption with other known quantities, like the vapor pressure, the equilibrium between gas and liquid, it was possible from that theory to get the best way how to determine the area of the absorbing layers.