Sound / by John Tyndall.

  • Tyndall, John, 1820-1893.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Sound / by John Tyndall. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    51/494 (page 29)
    series. Supposing the particle a to be driven by the prong of a timing-fork, or some other vibrating body, to- wards x, so as to be caused finally to occupy the position a' in the lowest row of particles. At the instant the excursion of a commences, its motion begins to be trans- mitted to b. In the next following moments b transmits the motion to c, c to d, d to e, and so on. So that by the time a has reached the position a', the motion will have been propagated to some point <?' of the line of particles more or less distant from a'. The entire series of particles between a' and o' is then in a state of condensation. The distance of o', over which the motion has travelled during the excursion of a to a', will depend upon the elastic force exerted between the particles. Fix your attention on any two of the particles, say a and b. The elastic force between them may be figured as a spiral spring, and it is plain that the more flaccid this spring the more sluggish would be the communication of the motion from a to b ; while the stiffer the spring the more prompt would be the communication of the motion. What is true of a and b is true for every other pair of particles between a and o. Now, the spring between every pair of these particles is suddenly stiffened by the heat developed along the line of condensation, and hence the velocity of propagation is augmented by this heat. Eeverting to our old experiment with the row of boys, it is as if, by the very act of pushing his neighbour, the muscular rigidity of each boy's arm was increased, thus enabling him to deliver his push more promptly than he would have done without this increase of rigidity. The condensed portion of a sonorous wave is propagated in the manner here described, and it is plain that the velocity of propagation is augmented by the heat developed in the condensation. Let us now turn our thoughts for a moment to the pro- pagation of the rarefaction. Supposing, as before, the