Experiment II. The same as before; only a circular piece of wood floated upon the surface of the water, on the centre of which the stream of the syphon was directed to prevent the current downwards.

A similar result was obtained in a different way by the following.

Experiment III.—Took an ale glass of a conical figure, 2 inches in diameter and 3 inches deep; filled it with water that had been standing in the room, and consequently of the temperature of the air nearly-Put the bulb of a thermometer to the bottom of the glass, the scale being out of the water: then, having marked the temperature, I put the red-hot tip of a poker half an inch deep into the water, holding it there steadily about half a minute; and as soon as it was withdrawn, I dipt the bulb of a sensible thermometer into the water about inch, when it rose in a few seconds to 180°.

These experiments all evidently agree in proving water to have a proper conducting power, independent of any internal motion.-It surely will not be said that any slight motion, unavoidably made at the beginning of an experiment, could continue with a powerful effect for upwards of an hour. However, to determine this matter, I made the two following experiments.

Experiment IV. Took the glass tumbler of the first experiment, and filled it half way with rain water, deeply tinged with archil; then filled it up with clear warm wa

ter,

ter, as related in the 2d experiment. The upper half was but just perceptibly tinged by the process and uniforinly so; it remained for an hour not visibly altered in this respect; though by frequently putting the bulb of a thermometer down to the middle, the colour at last rose in a small degree.

Experiment V. A glass tube near an inch in diameter, and 16 inches long, was half filled with a coloured solution of common salt in water, warm; a small thermometer was wholly immersed in it, and cold clear water carefully poured upod the whole, so as to fill the tube; the colour ascended very little, and continued invariable after the process of filling. The warm solution was of course made of greater specific gravity than the cold water.

To determine whether hot and cold water being suddenly mixed, and agitated, the hot would afterwards rise to the top, was the object of

Experiment VI. Air in the room 50°. About pint of water of 130° was poured into a cold tumbler glass, and immediately after as much water of 50°; the mixture was agitated for half a minute by a deal rod; after which an immersed thermometer stood at 85°, both at top and bottom; it was then set by in a still place for examination. TEMPERATURE.

From all these experiments it is evident, that water has a proper conducting power. In the last experiment, if: the particles of water during the agitation had not actually communicated their heat, the hot ones ought to have risen to the top, and the cold ones subsided so as to have made a material difference in the temperature. It is, however, equally evident, that water is a bad conductor of heat, probably as it is of electricity; the descent of the ..heat

1

heat in the second experiment is wonderfully slow; a slight agitation for one second would do as much to induce the equilibrium as standing still one hour. In repeating the third experiment, in a wine glass, I have several times known water an inch deeper to differ 50° in temperature from the incumbent water.

We must conclude, therefore, that the quick circulation of heat in water over a fire, &c. is owing principally to the internal motion excited by an alteration of the specific gravity; but not solely to that cause, as Count Rumford has inferred.

If it be proved that water conducts heat, it will scarcely be necessary to prove, that other fluids conduct it, and that they communicate it one to another :-the two following experiments shew that mercury conducts it, and that water and mercury reciprocally communicate it.

Experiment VII. Took a cylindrical glass tube, of 1 inch internal diameter, and put 13 inches in depth of mercury into it, and immersed the bulb and stem of a thermometer to the bottom, the scale as usual being above the liquid; then put 24 inches of warm water upon it by a syphon, and let it stand without agitation.

Experiment VIII. Into a tumbler glass, 2 inches in diameter, poured an inch in depth of mercury, and heated it to 110°; upon which was poured an inch of water at 50°, and then kept still.