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An instrument which makes a Fourier Series Analysis of a function by optical means has recently been completed. The function to be analyzed is supplied in the form of a variation in the density or in the width of the transparent portion of a photographic film. The analysis is performed by a direct evaluation of the integrals which form the coefficients in a Fourier Series, and the results are theoretically exact in the sense that the measurement of each harmonic is independent of the other harmonics which may be present in the function. The operation of the instrument is largely automatic, and is rapid enough so that 30 harmonics can be measured in about a minute and a half.1
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H. C. Montgomery (1938) studied this question.
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