Fourier Transform versus Grating Spectroscopy.

The essay shows that all passive spectroscopic instruments are interferometers relying on beam division and introduction of delay between beams to analyze spectra. When the number of beams is reduced to the minimum number, two, the energy throughput is a maximum, but Fourier transformation is necessary to translate the primary observations of complicated spectra into meaningful patterns. This step is easily made with modern digital computers, and these have given spectroscopists a windfall. For the first time, since the invention of the photographic plate, spectroscopists can exploit a powerful device which they did not have to invent for themselves.