Sound / by John Tyndall.

  • John Tyndall
Date:
1893
Catalogue details

Licence: Public Domain Mark

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

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    balloon crowding closely together ; the particles immedi- ately behind this condensation being separated more widely apart. We must, in short, be able to seize the conception that a sonorous wave consists of two portions, in the one of which the air is more dense, and in the other of which it is less dense than usual. A condensation and a rarefaction, then, are the two constituents of a wave of sound. § 2. Experiments in Vacuo, in Hydrogen, and on Mountains. That air is thus necessary to the propagation of sound was first experimentally proved by the illustrious Eobert Boyle. His experiment, after an interval of apparent oblivion, was revived by Hawksbee, in 1705. A bell was so fixed within the receiver of an air-pump that the bell could be rung when the receiver was exhausted. Before the air was withdrawn the sound of the bell was heard within the receiver; after the air was withdrawn the sound became so faint as to be hardly perceptible. An arrangement is before you which enables us to repeat this experiment in a very perfect manner. Within this jar, G g', fig. 4, resting on the plate of an air-pump, is a bell, B, associated with clockwork.1 After the jar has been ex- hausted as perfectly as possible, I release, by means of a rod, r r\ which passes air-tight through the top of the vessel, the detent which holds the hammer. It strikes, and you see it striking, but only those close to the bell can hear the sound. Hydrogen gas, which you know is four- teen times lighter than air, is now allowed to enter the vessel. The sound of the bell is not augmented by the 1 A very effective instrument, presented to the Royal Institution by Mr. Warren De La Rue.