The invisible part of the spectrum called the infrared has been known since the beginning of last century, and portions of it have been photographed for more than fifty years. Infrared photography is thus by no means a new subject. In 1931, however, discoveries were made which enabled it to be practiced by the general public with the ease of ordinary photography. At the present time the public is, consciously or unconsciously, very much concerned with photography. Not only does it use it as a hobby, but it relies upon it to an increasing extent for its knowledge of the world at large and for entertainment, and it has come to accept it as one of the most important instruments by which the scientist has been enabled to make the discoveries which have played the outstanding part in determining modern progress. Study of the infrared is now a very important part of the whole photographic field, and the interest in it is reflected by innumerable references in the popular, photographic, scientific and technical press. This literature is very widespread, and the time would now seem ripe for its material to be brought together within the confines of one volume.
The closest approach to perfection in the practice of an art or a science can be obtained most easily and with the greatest prospect of success through a knowledge of the principles basic to the practice. In this book, therefore, the attempt has been made to deal not only with what is known of infrared photography, but also with the underlying principles. It is hoped that as a result of this the photographer will be able to apply the subject intelligently to the varied problems which present themselves, and that those who are interested in utilizing its results will be aided in the appreciation of its possibilities and the interpretation of its findings.
The book is intended for the guidance of the practical infrared photographer, whether he is concerned with the commercial or artistic aspects of its subject or its applications in the scientific