Distinguished for his fundamental contributions to spectroscopic optics and method, molecular structure and spectrochemistry. His multiple-pass principle, which is a landmark in spectrometer design, has stimulated advances in all branches of spectroscopy, exemplified by his own contributions to infra-red and Raman spectroscopy and to atmospheric ozone spectrophotometry. Other contributions include echelette zone plates for far infra-red spectroscopy and a general-purpose spectroscopic light source unit. His method of recording atomic absorption spectra has provided a new approach to spectrochemical analysis and has been extended to the measurement of iaotopic abundances and atomic resonance line oscillator strengths.