This book by one of the world's foremost philosophers of science presented a striking new picture of the logical character of scientific discovery--a picture which does full justice to the liberating effect of the Einsteinian revolution in physics and its immense impact upon scientific thought in general. For this new English edition Dr. Popper did his own translation and has written 150 pages of entirely new text. Ernest Nagel considered this work "a first rate contribution to the logic of scientific method. The book contains a very interesting chapter on quantum mechanics, which performs one of the few sensible analyses of the Indeterminacy Principle which I have seen in print... The book is highly stimulating and contains much that is bed-rock for future work.