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1908 C. G. Knott Physics Earthquake Phenomena xi. 199 Although Rebeur Paschwitz had suggested the possibility, Oldham, of the Geological Survey of India, was the first clearly to establish the existence in the complete record of two distinct phases in the Preliminary Tremors.These will be distinguished as P and S.

1936 V. B. Macelwane in J. B. Macelwane & F. W. Sohon Introd. Theoret. Seismol. I. ix. 248 When it became clear that the P-waves were of the condensation-rarefaction type and the S-waves of the shear type, and individual earthquakes had been observed at a sufficient number of stations, attempts were made to draw up time–distance curves for the arrival times and to correlate these with the time of occurrence of the earthquake.

1966 McGraw-Hill Encycl. Sci. & Technol. (rev. ed.) XII. 152/1 The seismic body waves (P, S, and composite types like PS) have predominant periods in the range 1–15 sec, with P and S, respectively, at the short-period and long-period end of this range.

1990 P. Kearey & F. J. Vine Global Tectonics ii. 18 The Gutenberg discontinuity marks the core-mantle boundary at a depth of 2885 km, at which the velocity of P waves decreases abruptly.