ing that could be considered very surprising in this matter, yet I acknowledge fairly that it afforded me a degree of childish pleasure which, were I ambitious of the reputation of a grave philosopher, I ought most certainly rather to hide than to discover." I am sure we can dispense with the application of any philosophy which would stifle such emotion as Rumford here avowed.

Rumford carefully estimated the quantity of heat possessed by each portion of his apparatus at the conclusion of his experiment, and, adding all together, found a total sufficient to raise 26.58 lbs. of ice-cold water to its boiling-point, or through 180° Fahrenheit. By careful calculation he found this heat equal to that given out by the combustion of 2303.8 grains (= 4 oz. troy) of wax. He then determined the "celerity" with which the heat was generated, summing up thus: "From the results of these computations, it appears that the quantity of heat produced equably—or in a continuous stream, if I may use the expressionby the friction of the blunt steel borer against the bottom of the hollow metallic cylinder was greater than that produced in the combustion of nine wax candles, each threequarters of an inch in diameter, all burning together with clear, bright flames.

"One horse," he continues, "would have been equal to the work performed, though two were actually employed. Heat may thus be produced merely by the strength of a horse, and in a case of necessity this. heat might be used in cooking victuals. But no circumstances could be imagined in which this method of procuring heat would be advantageous, for more heat might be obtained by using the fodder necessary for the support of a horse as fuel."

This is an extremely significant passage, intimating, as it does, that Rumford saw clearly that the force of animals was derived from the food, no creation of force taking place in the animal's body.

By meditating on the results of all these experiments we are naturally," he says, "brought to the great question which has so often been the subject of speculation. among philosophers—namely, What is heat? Is there any such thing as an igneous fluid? Is there anything that with propriety can be called caloric?

"We have seen that a very considerable quantity of heat may be excited by the friction of two metallic surfaces, and given off in a constant stream or flux in all directions without interruption or intermission, and without any signs of diminution or exhaustion. In reasoning on this subject we must not forget that most remarkable circumstance that the source of the heat generated by friction in these experiments appeared evidently to be inexhaustible. [The italics are Rumford's.] It is hardly necessary to add that anything which any insulated body or system of bodies can continue to furnish. without limitation cannot possibly be a material substance; and it appears to me to be extremely difficult, if not quite impossible, to form any distinct idea of anything capable of being excited and communicated in those experiments, except it be MOTION."

With regard to the illustration which compared heat to water contained in a sponge, Rumford replied thus: "A sponge filled with water and hung by a thread in the middle of a room filled with dry air communicates its moisture to the air, it is true, but soon the water evaporates and the sponge can no

The conclusion drawn from these experiments by Rumford was contested by Bertholet, who stood forth as the champion "of the received theory of caloric." His arguments were fully set forth by Rumford, and totally overthrown. When the history of the dynamical theory of heat is completely written, the man who, in opposition to the scientific belief of his time, could experiment, and reason upon experiment, as Rumford did in the investigation here referred to, may count upon a foremost place. Hardly any thing more powerful against the materiality of heat has been since adduced, hardly anything more conclusive in the way of establishing that heat is what Boyle, Hooke and Locke considered it to be-motion.

And here we may refer to an observation of Rumford's which indicates at once his penetration and the limit of his knowledge. In 1778 he was engaged in experiments on the force of gunpowder, employing a musketbarrel, which he sometimes fired without any bullet and sometimes with one, two, three, or even four, bullets. Immediately after each discharge it was his practice to seize the barrel in his hand while it was wiped out, and he was astonished to notice that the barrel was always hotter when the charge consisted

of powder alone than when loaded with one or more bullets. Rumford rejected the notion that the gun was heated by the flame of the gunpowder, which he considered far too transitory to produce the heating effect observed. He referred that effect to mechanical concussion. Assuming heat to be " a more or less rapid vibratory motion among the particles of solid bodies," he concluded that when the powder alone was fired, the shock was "more vibrating or heavier" than when the combustion was obliged "to push slowly before it one or two balls which were anything but light.' thing but light." Had Rumford been aware of the entire bearing of the mechanical theory of heat, he would not, I think, have omitted to mention, in connection with this experiment, that the gunpowder urging the ball could not possibly generate the same amount of heat as when urging no ball. Rumford omitted all allusion to this, and Mayer was the first to discern the meaning of his observation.

Stimulated probably by Rumford, with whom he was personally connected at the Royal Institution, Davy took up this subject and enriched it by a beautiful and conclusive experiment. Ice is solid water, and the solid has only one-half the capacity for heat that liquid water possesses. A quantity of heat which would raise a pound of ice ten degrees in temperature would raise a pound of water only five degrees. Further, simply to liquefy a mass of ice an enormous amount of heat is necessary, this heat being so utterly absorbed or rendered "latent" as to make no impression upon the thermometer. What I am desirous of impressing on you at present is that, taking the materialists on their own ground, liquid water, at its freezing

of heat than ice at the same temperature.

Davy reasoned thus: "If I, by friction, liquefy ice, a substance will be produced which, according to the material theory, contains a far greater absolute amount of heat than the ice. In this case it cannot with any show of reason be affirmed that I merely render sensible heat which had been previously insensible in the frozen mass. Liquefaction will conclusively demonstrate a generation of new heat." He made the experiment, and liquefied the ice by pure friction. The experiment has been justly regarded as fatal to the material theory.

PHYSIOLOGICAL HEAT.

During the whole course of our lives we are continually inhaling and exhaling atmospheric air. Now, the nitrogen, which, as we have already learnt, constitutes four-fifths of the bulk of our atmosphere, does nothing toward the support of life. It is solely its companion element that sustains us. When we inhale, the oxygen passes across the cell-walls of the lungs and mixes with the blood, by which it is carried through the body. When we exhale, we pour out from the lungs the carbonic acid produced by the slow combustion of our bodies. To this slow combustion we owe our animal heat. Carbonic acid may be regarded as the rust of the body, which is continually cleared away by the lungs.

In every part of the body this combustion is going on. The blood is forced by the heart through the arteries to all parts of the system, and after passing through the capillaries it returns to the heart through the veins. The venous blood is much darker than the arterial blood-an effect due to the deoxidation of the

black venous blood yields up in the lungs the carbonic acid with which, through the combustion of the body, it was previously charged, the red color being thus restored.

Consider, then, all the fires in the world and all the animals in the world continually pouring their carbonic acid into the atmosphere. Would it not be fair to conclude that our air must become more and more contaminated and unfit to support either combustion or life? This seems inevitable, but it would be a conclusion founded upon half knowledge, and therefore wrong. A provision exists for continually purifying the atmosphere of its excess of carbonic acid. By the leaves of plants this gas is absorbed, and within the leaves it is decomposed by the solar rays. The carbon is stored up in the tree, while the pure oxygen is restored to the atmosphere: Carbonic acid, in fact, is to a great extent the nutriment of plants; and inasmuch as animals, in the long run, derive their food from the vegetable world, this very gas, which at first sight might be regarded as a deadly constituent of the atmosphere, is the main sustainer both of vegetable and animal life.

That the air which comes from the lungs is different in quality from that which goes into them may be shown by a simple experiment. Carbonic acid is warm, and therefore light, when freshly exhaled. It does not readily fall to the bottom of a vessel into which we breathe. But if the breath be chilled by sending it through a metal tube which passes through cold water, the carbonic acid may be collected in an open jar. A single expiration from the lungs suffices to fill a good-sized jar with the gas, which immediately quenches a lighted taper.