its usefulness has been touched. It has been surrounded with all the glamour and charms which the vivid imagination of the popular press is capable of bestowing. It has emerged from it as a proved useful weapon for the practical photographer and the investigator in the fields of science and technology. Further study cannot fail to find new uses for it. It is the purpose of this book to survey what has been done up to the time of writing, and to consider in detail the practical methods and underlying principles, a knowledge of which should aid in the proper application of the subject to the solution of new problems.
1. BABCOCK H. D., "Beyond the Red in the Spectrum," Smithsonian Inst. Rept. for 1930, 1931, 165-76.
2. BALY E. C. C., Spectroscopy, 3d ed., Longmans, Green, London, 1924- 27, vols. 1-3.
3. BRAGG Sir W., The Universe of Light, Macmillan, London and New York, 1933.
4. HERSCHEL W., "Investigation of the Powers of the Prismatic Colours
to Heat and Illuminate Objects; with Remarks, that prove the
different Refrangibility of radiant Heat. To which is added, an
Inquiry into the Method of viewing the Sun advantageously, with
Telescopes of large Apertures and high magnifying Powers," Phil.
Trans., 1800, 90, 255-83. "Experiments on the Refrangibility of the Invisible Rays of the
"Experiments on the Solar, and on the Terrestrial Rays that occasion Heat; with a comparative View of the Laws to which Light and Heat, or rather the Rays which occasion them, are subject, in order to determine whether they are the same, or different," part I, ibid., 293-326; part II, ibid., 437-538.
5. LECOMTE J., Le Spectre infrarouge, Presses Universitaires de France, Paris, 1928.
6. PLOTNIKOW J., "Ein Beitrag zur Geschichte der Ultrarotphotographie," Phot. Korr., 1938, 74, 54-6.
7. THOMPSON S. P., Light, Visible and Invisible, 2d ed., Macmillan, London, 1912.
8. TYNDALL J., Heat, Longmans, Green, London, 1890.