Although nearly three years have elapsed since the publication of this
work in Hungarian, it was decided to publish the English edition in the
same form as the original, apart from some minor modifications. Since,
recent research has been directed to the development of an exact theory
of non-linear irreversible processes; we suggest to readers interested
in similar tasks - such as the continuation of this boo- that they
should study some new publications: "On the most general form of the
Thermodynamic Integral Principle", Z. phys. Chem. 239 (1968) 133, and
particularly: "On the Governing Principle of Dissi- pative Processes",
Ann. Phys. 7 (1969) 23. I have to thank my wife and Mr. W.F.HEINZ for
the translation of the very concise Hungarian text. I also wish to
express my gratitude to Dr. L.KARADI and Mr. Gy. VINCZE for reading the
typescript with such care and to Mrs. A. R6sZLER, who typed the
manuscript with great patience. I am deeply indebted to Professor ISTVAN
SZABO for making this edition available so quickly and for including my
work in the "En- gineering Science Library". Finally, I would like to
express my thanks to Springer-Verlag for the excellent edition and to
the editorial staff for their readiness to meet my wishes.