London, Vintage, 2007. 304 pp. Paperback. Survey of the attempts in theoretical physics and mathematical physics to formulate unified field models connecting gravity with electromagnetic and strong and weak interactions. Conclusion is that after > 20 years (super)string theory has failed to adv.
Variational Principles In Dynamics And Quantum Theory
Mineola, NY, Dover Publications Inc. 2007. 3rd edition, 201 pp. Paperback. Co-author: Stanley Mandelstam. First published 1968, this Dover edition reprint of the third edition from 1979. Good.