438 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The remainder of the book is concerned with specialist instruments, accessories and techniques. Chapter $ includes the low resolution grating "Spectrosorter" the well known and versatile "IRGA" for the rapid determination of specific gases radiation thermometers and an automatic milk analyser. A particularly praiseworthy feature is a whole chapter devoted to the novel development of interferometric spectrometry: the conversion of the complex waveform to a suitable spectrum of a sample is usually achieved with the aid of paper tape fed to a high speed digital computer. Two commercial instruments, based on Michelson principles, are described but unfortunately there is no discussion of the practical difficulties that have slowed their development and the reader is referred elsewhere for reviews of fundamental work. In chapter 5 Dr. Martin recognises the manufacturers' obligation to anticipate the analyst's need for a wealth of accessories to cater for diversity of samples yet still furnish good quality spectra. He describes the principles and construction of many types of absorption cells - including micro and variable path - that are intended for a variety of operating conditions. Brief (half page) accounts are given of devices suitable for checking transmittance linearity provision for focusing with an external sample site or a reflecting microscope reflectance attachments reference beam attenuation electrical conversion of wavelength to wavenumber baseline, and trans- mittance to linear absorbance ordinate optical polarisation spectra long path multi-reflection cells for gases and low pressure yapours and desiccant systems. In a final chapter dealing with experimental methods and techniques, Dr. Martin briefly recommends special handling for organic, and especially aqueous, solutions and solids - using disc, mull, melt and film - and provides a slightly less sparse treatment of theroetical principles and commercial practice for Attenuated Total Reflectance spectra. Attention also is given to difference and derivative absorbance presentations. There is a non-critical list of the better known collections of reference spectra, a short appendix describing three crystal materials, a bibliography of 86 references cited in the text and a short but mostly adequate index. The book is couched in a condensed, almost telegraphic, style which conveys the impression of lecture notes but in a monograph of this type, such an approach is not unwelcome. Regarding instrument design there are frequent references to original papers and current manufacturers and there are many neat optical and mechanical diagrams illustrating features of principle or construction. In several important in- stances Dr. Martin provides a simple mathematical treatment: the physics of emission and detection of radiation,the optics of dispersion through prisms and gratings and the effect on transmittance of multiple reflections at interfaces, and the theoretical correlation between the Fourier transform of the interference pattern complex wave- form and a transmittance ratio spectrum for sample and reference beams. Altogether an interesting and authoritative monograph from an author much of whose professional life - in an earlier decade at the Government Laboratory and since 1946 with a leading instrument manufacturer - has been devoted to the develop- ment of ir spectrophotometry. G. F. PHILLIPS.