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)

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    vastly greater than that passed over in the same time by the particle itself. The excursion of a' may be of micro- scopic minuteness, while the distance to which the motion is transferred during the time required by a' to perform this small excursion may be many feet, or even many yards. § 10. Ratio of Specific Heats of Air deduced from Velocity of Sound. Having grasped this, even partially, I will ask you to accompany me to a remote corner of the domain of physics, with the view, however, of showing that remote- ness does not imply discontinuity. Let a certain quan- tity of air at a temperature of 0°, contained in a perfectly inexpansible vessel, have its temperature raised 1°. Let the same quantity of air, placed in a vessel which permits the air to expand when it is heated—the pressure on the air being kept constant during its expansion—also have its temperature raised 1°. The quantities of heat em- ployed in the two cases are different.1 The one quantity expresses what is called the specific heat of air at constant volume; the other the specific heat of air at constant pressure. It is an instance of the manner in which ap- parently unrelated natural phenomena are bound together, that from the calculated and observed velocities of sound in air we can deduce the ratio of these two specific heats. .Squaring Newton's theoretic velocity, squaring also the observed velocity, and dividing the greater square by the less, we obtain the ratio referred to. Calling the specific heat at constant volume Cv, and that at constant pressure O ; calling, moreover, Newton's calculated velocity V, and the observed velocity V, Laplace proved that Cp V'2 17 = Vr 1 See Heal a Mode of Motion, Sixth ed. Lcct. V.