Although text-books of science may appear to the general reader to be "very dry" material, there is no doubt that, when scientific facts and theories are put into everyday language, the general reader is genuinely interested. The reception accorded to the present author's Scientific Ideas of To-day bears out this fact. While that volume explains, in non-technical language, the latest scientific theories, it aims at giving a fairly full account, which, of course, necessitates going into a great deal of detail. That the book has been appreciated by very varied classes of readers is evident from the large numbers of appreciative letters received from different quarters. But the author believes that if the story of modern science were told in a still more popular style, it would serve a further useful purpose. For there are readers who do not care to go into details, and yet would like to take an intelligent interest in the scientific progress of the present day. Some of those readers do not wish to trouble about names and dates, while the mere mention of rates of vibration and such-like is a worry to them. They wish a book which they may read with the same ease as an interesting novel. Hence the form of the present volume.

The author is indebted to Professor James Muir, M.A., D.Sc., of the Glasgow and West of Scotland Technical College, and to H. Stanley Allen, M.A., D.Sc., Senior Lecturer in Physics at King's College, University of London, for very kindly reading the proof-sheets. The author is indebted further to Professor Muir in connection with some of the illustrations, and for others to Dixon and Corbitt and R. S. Newall, Ltd., Glasgow; Siemens Schuckert Werke, Berlin.