Archimedes was an Ancient Greek mathematician who came up with the Archimedes principle.
According to Dr. McKay, legend has it that he came up with the idea for his principle when he was sitting in a bath, leading him to have the revelation. Instead of working to find a solution, he would relax until the solution came to him. McKay had that kind of revelation a few times during his work in the Atlantis expedition. (SGA: "Home", "Broken Ties")
Sheppard initially confused McKay's reference to this scientist with another Archimedes, a Greek member of the Atlantis expedition who once had a crush on Teyla