The first part of this paper was occupied with the discussion of the validity of Newton's Theory of the Propagation of Sound. In order to discover the velocity of sound, Newton supposes a series of particles ranged in a straight line to be set to vibrate all equally and isochronously, but the epoch of vibration to vary gradually along the line; and he then investigates the circumstances under which such a vibration is possible. The true result of the investigation is this,—that if the two extreme particles be kept vibrating by some external influence, and if all the intermediate particles be fairly started with the velocities appropriate to their positions in the series, the constrained vibrations of the two extreme particles, aided by the elasticities of the intermediate parts, are sufficient to maintain the vibrations of those parts.