To write a handbook of methods is surely to invite criticism, as has already been said several times. On the other hand, there is a great need for methodological manuals in all fields of science. It was therefore decided to compile this book, written in good faith to help scientists, teachers and students who will, it is hoped, use it and judge it good. To be useful to the reader, such a manual must provide a broad review of the methods available and describe them in sufficient detail to permit preliminary selection and judgement. It has to give - at least for selected methods - a suffi­ ciently detailed description of the equipment and procedure as to be to some extent self-contained. It must assume a critical standpoint as regards the theoretical basis of the methods, the significance of results, and their errors and limitations. It must also furnish examples, pertinent numerical tables, and very complete references. All this and much more is expected of a good manual of methods.