s this subject is being dealt with for the first time in these Reports, it seems desirable to touch briefly on the historical side and to cover the ground-A work fairly thoroughly, indicating the present trend of progress and lines of future development of the applications of spectroscopy to combustion without dealing in detail with all the latest original papers.It is convenient to divide the subject into four main sections.. The first deals with the more obvious approach to the subject, the visible and ultra-violet emission spectra of flames, explosions, cold flames, etc. The second section is devoted to absorption spectra, and the third section to the infra-red region. The last section, on the subject of energy considerations, is concerned with the large number of indirect but extremely fruitful applications of spectroscopy to combustion problems, such as the calculation of dissociation energies, specific heats, quantitative considerations of the lifetimes of activated molecules, and temperature measurement. 8 2. E M I S S I O N SPECTRA * Leverhulme Research Fellow.