Distinction is made between continuous and discontinuous variables in frequency distributions. Histograms, frequency curves, and cumulative curves are discussed in relation to each other. On the basis of these relations an attempt is made to explain why histograms vary with the grade scale used in mechanical analysis, while cumulative curves do not. The disadvantages of histograms may be avoided by a simple graphic method for obtaining a continuous frequency curve independent of the grade scale. This curve is obtained by graphic differentiation of the cumulative curve, and is expressed in terms of the Wentworth descriptive grade scale. The analytic scale for obtaining the data is, however, shown to he independent of the descriptive scale units. It is suggested that in analyzing sediments, as many points as necessary be determined along the cumulative curve, to reduce errors of smoothing to a minimum.

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