Sound : a course of eight lectures delivered at the Royal Institution of Great Britain / by John Tyndall.

  • John Tyndall
Date:
1869
Catalogue details

Licence: Public Domain Mark

Credit: Sound : a course of eight lectures delivered at the Royal Institution of Great Britain / by John Tyndall. Source: Wellcome Collection.

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    the motion excited in the olfactory nerves by the efflu- vium of a rose, which announces itself in the brain as the odour of the rose. It is the motion imparted by the sunbeams to the optic nerve which, when it reaches the brain, awakes the consciousness of light; while a similar motion imparted to other nerves resolves itself into heat in the same wonderful organ.* The motion here meant is not that of the nerve as a whole; it is the vibration, or tremor, of its molecules or smallest particles. Different nerves are appropriated to the transmission of different kinds of molecular motion. The nerves of taste, for example, are not competent to transmit the tremors of light, nor is the optic nerve competent to transmit sonorous vibration. For this latter a special nerve is necessary, which passes from the brain into one of the cavities of the ear, and there spreads out in a multitude of filaments. It is the motion imparted to this, the auditory nerve, which, in the brain, is translated into sound. We have this day to examine how sonorous motion is produced and propagated. When a flame is applied to this small collodion balloon, which contains a mixture of oxygen and hydrogen, the gases explode, and every ear in this room is conscious of a shock, to which the name of sound is given. How was this shock transmitted from the balloon to your organs of hearing ? Have the exploding gases shot the air-particles against the auditory nerve as a gun shoots a ball against a target? No doubt, in the neighbourhood of the balloon, there is to some extent a propulsion of particles; but air shooting through air comes speedily to rest, and no particle of air from the vicinity of the balloon reached the ear of any person here present. The * The rapidity with which an impression is transmitted through the nerves, as first determined by Helmholtz and confirmed by Du Bois Raymond, is 93 feet a second.
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