Vibrations of a

in it.

after it is depressed by the elasticity of the vapour formed. If we then raise or lower the external level of the mercury, the interior columu will rise or fall exactly as much in the tube; and thus, according as the space remaining at the top of the tube is diminished or increased, a part of the vapour will be precipitated, or fresh vapour will be formed: but, the temperature remaining the same, the elasticity will not alter.

Now let us suppose, that a sonorous body begins to visonorous body brate in such a medium; each of its vibrations will diminish the space in one direction, and increase it in the opposite. Thus on one side there will be a small quantity of vapour reduced to the liquid state, and on the other a small quantity of liquid will assume the state of vapour. These condensations and dilatations will take place close to the sonorous body in the small extent of its vibrations, but will not be produced beyond this. Thus the motion will not be propagated through the rest of the fluid mass, and consequently the sound will not be transmitted.

If we suppose these to disen gage heat,

Let us next suppose, that the sonorous body, in compressing the vapour by its rapid vibrations, disengages from it mechanically a certain quantity of heat. This supposition is by no means improbable, for we know, that vapour gives out a great deal of heat in its condensation. The va pour of water, for example, according to the experiments of Watt, in returning to the liquid state gives out a quantity of heat, that is capable of raising the temperature of the sound should water thus produced to 525° [977° F.]. If we take this cirbe produced in cumstance into consideration, the effects of the sonorous body on vapour will no longer be the same: the portions it compresses will preserve their elastic state, notwithstanding the diminution of the space, in consequence of the heat evolved, which instantly increases their elasticity. On the contrary, in the portion dilated the diminution of tempera ture, preventing a new evaporation, diminishes the elasticity. The phenomena produced near the sonorous body therefore are of the same nature, as if the vapour became a permanent gas. There will be successive and momentary augmentations and diminutions of elasticity, the effect of which will be transmitted step by step throughout the whole

of

of the fluid mass, so as to permit sound to be produced and transmitted in it.

Experiments on the production of sound in vapour there. This may be fore are calculated to decide the question, whether heat be brought to the test of expert really evolved in an aeriform medium by the effect of the vi→ ment, brations of sonorous bodies, as we see it in general extricated by any rapid compression. Thus we may subject to decisive proof the ingenious idea of Mr. Laplace, by which he has found means of reconciling the mathematical theory of the transmission of sound in air with the results of experience, taking into account the heat evolved: for, if the effect he supposes do not take place, the vibrations of sonorous bodies in vapour should not produce any sound; and, if they do produce sound, it can be only in consequence of the evolution of heat.

vapour.

scribed.

Induced by these motives, I made some experiments on Sound was the subject, which completely succeeded. then repeated produced in them in a more perfect manner, in the philosophical apart ments at Arcueil, with my friend Amadeus Berthollet. Mr. Berthollet, and Mr, Laplace were present at these experi ments, and themselves verified the facts I am going to relate. We took a glass globe that held 36 litres [near 38 wine Apparatus dequarts]. Its orifice was closed by a well made cock, so that a vacuum might be made in it, which it preserved with great accuracy. To this cock another could be screwed; so that, by pouring a liquid into the space between them, and closing both, this portion of liquid could be afterward introduced into the globe, without admitting any air from without. The sonorous body was a small beil, suspended within the globe by a slender string fastened to the lower cock.

in a vacuum no sound.

A yacuum was first made within the apparatus to the Experiment. greatest nicety, and even so as to exhaust a great part of the hygrometrical water, that might have existed in the globe, which howeyer was very dry, Then, holding the globe by the cock, we set the bell in motion, so us to satisfy ourselves, that the clapper struck very forcibly against the sides: yet, with all the attention we could bestow, even close to the globe itself no sound could be perceived; so that there was no perceptible sound in a vacuum, agreeably to the experiments of Hawksbee, and all other philosophers,

We

In aqueous vapour sound

produced

proportional to its density,

In vapour of alcohol sound

louder.

Experiment in vapour of ether.

Distance at

which the sound was heard in atmospheric air.

We then jutroduced into the globe, in the way I have `described, a sufall quantity of water, part of which was converted into vapour. The sound immediately began to be perceptible, though the density of this vapour was extremely small, the temperature being only 19° [66-2° F.]. To increase it, an excess of water was admitted into the globe, and it was placed in a stove at the temperature of 46 [114-8° F.]. The sound then became very perceptible: it could be heard without stooping down to the globe, and even out of the stove through the door. Some water still remained in the globe, so there can be no doubt, that the sound was produced and transmitted in the aqueous vapour.

When the globe was taken out of the stove, the temperature quickly fell: a great part of the vapour therefore, which had been raised in consequence of the temperature, was necessarily precipitated; and accordingly the sound appeared very evidently diminished.

Without any alteration in the apparatus, we introduced the same quantity of alcohol, as we had before of water. The specific gravity of this alcohol was 0.823. The vapour from this mixture possessed of course greater density and elasticity than that of water at the same temperature; and accordingly the sound was much more perceptible: it was heard from one extremity to the other of the rooms that form the philosophical apartments at Arcueil. Sound therefore is produced and transmitted in the vapour of alcohol.

As a last experiment we tried the vapour of ether. This particularly excited our curiosity, on account of its great elastic force and density, which are known to be very considerable; two circumstances, that must contribute to increase the intensity of the sound. We begun with drying the globe, because the moisture would have diminished the tension of the ether; and then allowed the atmospheric air to enter freely, till it was in equilibrio with the external pressure, which was 0-7613 [29-951 inch.]; and, carrying it into a long walk in the garden, we found, that the sound of the bell was sensible to the distance of 145 met. [158.5 yd:]: beyond this it was so faint, that the

perception

duced.

which the

perception of it was not sufficiently certain. The temperature was 17.75° [63-95° F.]. Having measured by this experiment the intensity of the sound produced in atmospheric air, we again made a vacuum in the globe, and introduced into it a sufficient quantity of sulphuric ether, to leave a surplus above what the temperature could convert into vapour. The specific gravity of this ether was 0.759. The elastic Ether introforce of its vapour, measured by introducing it under a ba- Elasticity of rometer freed from air, was 0.3549 met. [13-963 inches], at its vapour. the temperature of 17.75° [63-95° F.]. The globe being filled with this vapour, it was carried to the same place as in the preceding experiment; when we found, that the sound was perceptible to the distance of 131.5 met. [1437 Distance at yards]. This conclusively proves in the most convincing sound was manner, that sound is produced and transmitted in vapour, heard. as well as in a permanent gas. But we have proved, that This proves the momentsthis can take place only from the effect of instantaneous vary variations riations of temperature, occasioned by the vibrations. It of temperature evidently follows therefore, that this cause really exists; caused by viand that, according to the judicious remark of Mr. Laplace, cording to the it becomes indispensable for us to pay attention to it in the theory of La. place. mathematical theory of the propagation of sound; though we cannot directly verify it by the application of the ther mometer, because this instrument can no more be affected by these successive and momentary variations of heat, than the barometer is by the momentary variations of elasticity, that take place in the production of sound, and of which every one notwithstanding acknowledges the existence.

brations ac

III.

Experiments to prove, that Fluids pass directly from the Stomach to the Circulation of the Blood, and thence into the Cells of the Spleen, the Gall Bladder, and Urinary Bladder, without going through the Thoracic Duct. By EVERARD HOME, Esq. F. R. S*.

HAVING on

AVING on a former occasion laid before the Society Fluids pass some experiments, to prove, that fluids pass directly from from the sto

mach into the the cardiac portion of the stomach, so as to arrrive at the cira blood, enlation of the blood without going through the thoracic duct, the only known channel by which liquids can arrive there; the present experiments are brought to confirm that opinion; but in stating them, I wish to correct an errour, I was led into, in believing that the spleen was the channel, by which they are conveyed.

but not

through the spleen.

The passage

might be found

At the time I made my former communications*, I was by tying the conscious, that the facts I had ascertained were only sufficient thoracic duct. to open a new field of inquiry; but as I might never be able to make a farther progress in an investigation, beset with so many difficulties, I thought it right to put them on record. Since that time I have lost no opportunity of devising new experiments to elucidate this subject; and the circumstance of Mr. Brodie, the assistant of my philosophical as well as professional labours, having tied the thoracic duct in some experiments which will come before the Society, suggested to me the idea, that, if the thoracic duct was tied, and proper experiments made, there could be no difficulty in ascer taining whether there was any other channel between the stomach and the circulation of the blood.

Exp. 1, on a rabbit.

With this view I instituted the following experiment, which was made on the 29th of September, 1810, by Mr. Brodie, assisted by Mr. William Brande and Mr. Gatcombe. I was unavoidably prevented from being present during the time of the experiment.

Exp. 1. A ligature was passed round the thoracic duct of a rabbit, just before it enters at the junction between the left jugular and subclavian veins: an ounce of strong infusion of rhubarb was then injected into the stomach. In three quarters of an hour some urine was voided, in which rhubarb was distinctly detected, by the addition of potash. An hour and a quarter after the injection of the rhubarb the animal was killed: a dram and half of urine was found in the bladder highly tinged with rhubarb, and the usual alteration of colour took place on the addition of potash. The coats of the thoracic duct had given way opposite the middle dor sal vertebra, and nearly an ounce of chyle was found effused into the cavity of the thorax, beside a considerable quantity

See Journ. vol. XX, p. 374, and XXI, 108.