Why Beauty is Truth
Stewart shows how Sophus Lie applied the notion of a group to continuous systems. He describes the work of Einstein, as well as the development of quantum theory, showing how symmetry has a natural place in modern physics. There is also a chapter on Edward Witten and Superstring theory. Stewart also clearly has a soft spot for quaternions and octonions, showing how these almost forgotten structures may yet play an important part in physics.
The book gives prominence to biographies of the mathematicians concerned, and some people might feel that there isn't enough maths, however I felt that Stewart struck the right balance, and so kept the book accessible to a wide readership.