We started our work on theoretical methods in the phys ics of high pressures (in connec- tion with geophysical applications) in 1956, and we immediately encountered many problems. Naturally, we searched the published Iiterature for solutions to these problems but whenever we failed to find a solution or when the solution did not satisfy us, we attempted to solve the problern ourselves. We realized that other investigators working in the physics of high pres- sures would probably encounter the same problems and doubts. Therefore, we decided to write this book in order to save our colleagues...