The experiments recorded in the accompanying paper2 were instituted for the purpose of ascertaining the thermal effect produced by the passage of air from a high to a low pressure across a porous plug. It is shewn that a cooling effect takes place, and that the amount of this effect is sensibly proportional to the difference of pressure on both sides of the plug. With carbonic acid the cooling effect is found to be greater than with air, whereas in the case of hydrogen the cooling effect, inferred from some preliminary experiments, appears to be only one thirteenth that of atmospheric air. A remarkable result has been obtained from the interdiffusion of two different gases – the thermal effect accompanying the interdiffusion of carbonic acid and air was found to be a diminution of temperature amounting to 2° Cent.3 It is to be hoped that the authors4 will fulfil their promise of making more exact experiments on this important point. The above experiments and the theoretic deductions drawn from them appears to me calculated to increase our knowledge regarding the nature of Heat & would therefore recommend their publication in the Philosophical Transactions.5
John Tyndall
31 Oct. 18546
RS RR/2/239
The Secretary of the Royal Society: this letter was addressed to ‘The Secratary of the Royal Society’ (Tyndall misspelled ‘Secretary’). At the time, the Secretary of the RS was George Gabriel Stokes.
The experiments … accompanying paper: see letter 0981, n. 8.
Cent.: centigrade.
the authors: Joule and Thomson.
recommend … Philosophical Transactions: it is unclear if Joule and Thomson undertook the further experimentation recommended by Tyndall. Their paper was eventually published in the Phil. Trans. (see 0981, n. 8).
31 Oct. 1854: the following was written in another hand that appears in the top right corner of the reverse side of the letter: ‘31. Oct. 1854 | Chpt. By Dr. Tindal | on Messrs Thomson & | Joule’s paper.’
Please cite as “Tyndall0994,” in Ɛpsilon: The John Tyndall Collection accessed on