ABSTRACT
Few branches of growing physics have suffered worse in presentation than the quantum theory, particularly because for practical purposes mathematical physicists who are working at it use mathematics up to the very last moment when they see whether or not their mathematical predictions are verified; and when they try to put these mathematics into words they sometimes talk nonsense. But in addition, there has been an undue tendency in certain popular books to exploit its paradoxical and negative sides, whereas its positive side gives information additional to that of classical physics, which is just as real. In order to understand even what the quantum theory is about, one must study the historical development of physics. A great deal of elementary chemistry is explained quantitatively by means of quantum mechanics in a way which few years ago seemed quite impossible to a philosopher as Broad, and to others who think on positivist lines, even if they do not call themselves positivists.
