velocity less than that with which a man reaches the ground when he jumps off a table. With the same omissions, Mallet gives the following table, showing a general decrease in the maximum velocity as the distance from his epicentre increases:-- Polla. Padula. Certosa. Moliterno. Viscolione. Sarconi. Distance in miles 4.0 19.0 19.0 29.4 30.0 30.8 Max. vel. in ft. per sec. 13.2 12.9 11.5 11.8 11.0 9.8 On the north side of the epicentre we have:-- Potenza. Monticchio. Barielle. Distance in miles 17.3 27.1 28.2 Max. vel. in ft. per sec. 12.3 11.8 11.6 It is not impossible that the high calculated velocities at Tramutola and Saponara were partly or entirely due to the impulse from the Montemurro focus. If we take 4 inches for the amplitude of the largest variation, and 12 feet per second for the maximum velocity, and assume the motion to have been of a simple harmonic character, the period of a complete vibration would be less than one-fifth of a second.[17] Now, we know from seismographic records that this is roughly the period of the small tremors that form the commencement of an earthquake-shock, while the period of the largest vibrations may amount to as much as one or two seconds. We may therefore conclude either that the assumption of simple harmonic motion is incorrect, or that the maximum velocity is too great, or more probably perhaps that the amplitude is too small.[18] SOUND-PHENOMENA. Mallet was one of the first seismologists to realise the significance of the earthquake-sound; and he attended closely to the subject, though finding the sound even more elusive of precise observation than the shock. The chief result obtained by him was the comparative smallness of the area over which the sound was heard. He estimates it at little more than 3,300 square miles, or about one-twelfth of that over which the shock was felt. It extends north and south from Melfi to Lagonegro, and east and west from Monte Peloso to Duchessa and Senerchia. The sound was thus confined to the region in which the shock attained its most destructive character. Towards the north and south ends of the sound-area all observers described the sound as a low, grating, heavy, sighing rush, lasting from twenty to sixty seconds, some adding that it was also of a rumbling nature. Near the centre and the east and west boundaries, the sound was distinctly more rumbling; it was shorter in duration, and began and ended more abruptly.