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NATURAL LAW OF CIRCULATION.*

BY PROFESSOR JOSEPH LECONTE, OF THE UNIVERSITY OF CALIFORNIA.

The law of circulation, or cyclical movement-of movement in everrecurring cycles, returning each upon itself-of flux and reflux, has ever been regarded by philosophic thinkers of all ages and countries as the most fundamental and universal law of things material. Solomon says:† "One generation passeth away and another generation cometh; but the earth abideth forever. The sun also ariseth and the sun goeth down, and hasteth to his place where he arose. The wind goeth toward the south, and turneth about unto the north; it whirleth about continually, and the wind returneth again according to its circuits. All the rivers run into the sea; yet the sea is not full: unto the place from whence the rivers came, thither they return again. There is no new thing under the sun." My object this evening is to give some illustrations of this familiar truth and to show its universality, but at the same time to show that this cyclical movement is not vain, but that in every case there is an important work accomplished.

The function of science is not only to discover new truth, but also, and equally, to give clear and perfect form to old truth-to change popular notions into positive knowledge-to give definite rational form to the vague intuitions of the popular mind. This it does by means of its admirable methods. As is the eye among the sense organs, so is science among the means of acquiring knowledge. As the vague perceptions of the external world received through the other senses are changed into full, clear and precise knowledge only through the complex and delicately adjusted mechanism of the eye, even so the dim foreshadowings, the vague intuitions, the partial anticipations of truth by the popular mind and, even by philosophic genius, take clear outline and permanent form only through the complex and exquisitely delicate methods of science. My object, therefore, more definitely stated, will be to give scientific illustrations of this great truth dimly seen by thinkers of all ages. In doing so, I have chosen the more informal method of extemperaneous delivery, hoping that what I lose in grace and felicity of expression, I may gain in directness of personal address.

*This article, given on several occasions as an extemporaneous lecture, is now, January, 1871, written out for the first time. In doing so, I have attempted to retain, as much as possible, the style of extemporaneous delivery.

†Eccles. Chap. 1, 4-9.

CIRCULATION.

1. Air and Water. The circulation of air and water is so familiar, that it may seem unnecessary to refer to it. On that very account, however, I have chosen it as my first illustration, in order thus, at the outset, to fix clearly in the mind the idea of perpetual circulation.

The earth is everywhere and at all times both receiving heat from the sun and space, and radiating heat back into space-is all the time both heating and cooling. The amounts received and expended by the whole earth are equal; so that the mean temperature of the whole earth, leaving out of view those slow, secular changes of which geology tells us, may be regarded as constant. But it is far otherwise when we regard different portions of the earth's surface. The equator receives far more heat than it radiates, while the poles radiate more heat than they receive. Thus the earth may be regarded as heating at the equator and cooling at the poles. The tendency, therefore, is for the equator to grow hotter and hotter and the poles to grow colder and colder, at least to limit far beyond their present condition. But by the law of circulation, nature strives ever towards an equilibrium, which she never wholly attains. This condition of extreme diversity of temperature is prevented by exchange of air and water between poles and equator. Currents of air from equator to poles and counter currents from poles to equator, deflected by rotation of the earth, reflected from mountain chains, meeting and mingling with each other and contending for mastery, give rise to the almost infinitely variable winds, which," whirling about continually," have as yet baffled the efforts of science to bring them under the perfect dominion of law. Similarly, currents of water from poles to equator and counter currents from equator to poles, deflected by rotation of the earth, reflected by continents and submarine banks, produce those ocean streams the knowledge of which is so important to commerce, but the theory of which is still so imperfect.

Again, land and sea may be regarded as the two parts of a distilling apparatus, the sea being the boiler and the land the condenser. By the power of sun heat, water rises as vapor from the ocean, is condensed by high mountains as snow and rain, and runs back again by rivers to the ocean, to recommence the same eternal round. "To the place whence the rivers come thither they go again."

2. Glaciers and Icebergs. In certain countries, where the mountains rise into the regions of perpetual snow, and where other conditions are favorable, we find large masses of solid ice filling the mountain valleys, reaching down below the line of perpetual snow, below the mean line of thirty-two degrees, into the genial regions of cultivated fields. Moving ever downwards, ploughing up the earth, scoring, planing, grinding to dust the hardest rocks, moving ever downwards yet nev r passing a certain point, where the waste balances the downward motion. Such evermoving masses of solid ice or ice streams are called glaciers. I will not stop to explain the theory of this wonderful motion, or show the powerful effect which glaciers have now, and still more have had in former times, in determining the forms of mountain chains, as may be plainly seen on the slopes of our own Sierras, although few subjects are more interesting both to the physicist and the geologist. My object now is only to show that both the existence of glaciers and their motion is the necessary result of the law of circulation.

In regions where glaciers occur, the amount of snow which falls on the mountain tops is always far greater than the waste by melting and

evaporation in the same area. If there was no law by which this excess was removed, the accumulation of snow would continue apparently without limit. But this indefinite accumulation is prevented and the excess of snow is returned into the general circulation of meteoric waters by the formation and the downward motion of glaciers which carry it into lower and warmer regions where the waste may be equal to the supply. Again, the snow which falls in polar regions is far greater than the waste in the same region. Without some means of removal of this excess, there seems no limit to the accumulation; there seems no avoiding the conclusion that all the waters on the earth would eventually accumulate as snow in these regions. But nature abhors indefinite accumulation as she does a vacuum or indefinite exhaustion, and tends ever toward equilibrium. This indefinite accumulation is prevented by the formation and drifting of icebergs. The universal ice sheet of polar continents, moving slowly coastward, reaches and runs out into the sea. Great fragments are here broken off by waves and tides, and, floating away as icebergs, are taken by oceanic currents and carried southward into warmer seas, where they are melted and again returned into the general circulation of meteoric waters.

3. Organic Kingdom and the Atmosphere. The next example of circulation which we give is far more subtle and beautiful. It is the circulation of certain chemical elements, called organogens, between the organic kingdom and the atmosphere. We will show, first, the necessity, and then the process, of this circulation.

The food of plants, with the exception of the small quantity of mineral matter taken from the earth and left by combustion as ash, consists entirely of carbonic acid (CO,), water (HO) and ammonia (NH).* The whole organic matter of the plant is made from these materials. Now, all these exist in the atmosphere; and it is from this source entirely that plants derive them. They take them, either directly from the atmosphere by their leaves or in the form of rain water by their roots; but, with the exception of water, the whole supply of these substances is extremely limited, and, if not restored, would be speedily exhausted. Only about one two-thousandth by volume, or one one-thousand six hundred and sixty-sixth by weight, of the atmosphere consists of carbonic acid, and the quantity of ammonia is so small as to be scarcely detectible. Now, according to the experiments of Boussingault,† one acre of luxuriant vegetation takes from the atmosphere, per annum, about a half ton (one thousand one hundred and twenty pounds) of carbon, which is equivalent to nearly two tons (four thousand one hundred and six pounds) of carbonic acid. Estimating the weight of the atmosphere as one ton per square foot, the weight of carbonic acid in the atmosphere resting on an acre of ground is about twenty-six tons. acre of vigorous vegetation would exhaust this in about fourteen years. If the earth were entirely covered with vigorous vegetation, the whole stock of carbonic acid, if unrenewed, would be exhausted in that short space of time. It is true that the earth's surface is not covered in every part with vigorous vegetation; many parts being, in fact, desert. It is true, too, that three-fourths of the earth's surface is covered with ocean, although it is by no means certain that the amount of vegetation in the ocean, for equal are s, is much, if at all, less than that of the land; for the ocean teems with animal life, and animal life is entirely dependent

I have preferred to use the old notation, as being more familiar. † Johnson's Agricultural Chemistry.

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upon, and must be proportioned to vegetation. Yet, making every allowance for these facts, it is quite evident that the carbonic acid in the air, if unrenewed, could not possibly last but a very few generations. It is probable that the ammonia would be exhausted in an equally short time; for although the consumption of ammonia by plants is much less than of carbonic acid, yet the quantity of this kind of plant food in the air is also more limited. These necessary ingredients of plant food being exhausted, of course the vegetable kingdom would perish, and with it also the animal kingdom which it supports, and thus all life would cease on the surface of our earth. But as no such sad catastrophe occurs, there must be a constant supply of an equal amount of these substances to the atmosphere.

The sources of this supply are four in number, viz: 1. Combustion— every chimney in this city, every lamp and gas jet in this building, is pouring carbonic acid into the atmosphere; 2. Animal respiration-every nostril in this crowded room is also pouring into the air carbonic acid, formed by the concealed fires within the body; 3. General decay of organic matter, vegetable and animal, everywhere-every manure heap is a smouldering fire, giving carbonic acid slowly to the air; 4. Carbonated springs and volcanoes-these also give to the air carbonic acid, derived from the interior of the earth. But these are not supplies of new carbonic acid, not previously existing in the atmosphere. On the contrary, these processes only return to the air what was before taken from it. In respiration we return to the air what was taken from it, perhaps, by the last wheat crop. General decay is everywhere returning to the air what was taken from it by a previous generation. Combustion of coal returns to the air carbonic acid which was taken from it millions of years ago by the vegetation of a previous geological epoch; even carbonated springs and volcanoes probably also only return to the air carbonic acid which was taken from it at a still more remote period. The whole of the carbon and carbonic acid in and about our earth once existed in the atmosphere. All these processes are therefore only the evidences of the circulation of carbon. The same is true of ammonia. The principal source of supply of this kind of plant food is general decay; but this only returns what was before taken by plants from the atmosphere, and is therefore evidence of circulation.

Now, of the several sources of supply of plant food mentioned above, there are two which may be regarded as the regular sources upon which nature relics to keep the supply constant, viz: general decay and animal respiration. Each of these gives rise to a peculiar circulation of a very interesting kind.

(a) Decay. As already stated, the food of plants consists of carbonic acid, water and ammonia (CO,HO and NH,), or of water, containing carbonic acid and ammonia. In other words, it consists of rain waterfor rain water always contains carbonic acid and ammonia. This solution, taken up principally by the roots, passes upwards through the trunk and limbs to the extremest sprays, seeking ever the light, and enters the leaves. There, in the green leaves of plants and under the influence of sunlight, takes place the most wonderful change which is known, perhaps, in the whole course of nature. Carbonic acid, water and ammonia, by the vital force residing in the leaf, or, may we not say, by the power of sunlight, under the peculiar conditions existing in green leaves, are forcibly decomposed-violently dismembered, as it were,

by a superior force; and the dismembered fragments, after the rejection of superfluous parts, are forced into unnatural union, against the ordinary laws of chemistry, to form organic matter. The sap rises to the leaves a solution of carbonic acid and ammonia, it descends from the leaves a solution of dextrine, sugar and protoplasm-it rises mineral matter, it descends organic matter-it rises dead matter, passive under the sway of physical and chemical forces; it descends living matter, endowed with vital, organizing forces, which seem superior to ordinary physical and chemical forces. Here, then, in the green leaves of plants and under the influence of sunlight, we have the starting point of life. Here we have, taking place every day, before our very eyes, the miracle of the creation of organic matter and the origin of life force. All the organic matter in the world is made just here, and under these conditions. Animals have no power to make organic matter from mineral matter, but feed upon plants and appropriate the organic matter already made by them.

Now, organic matter consists of carbon, hydrogen, oxygen and nitrogen (CHO and N), in peculiar combination. These elements the plant derives from its food, carbonic acid, water and ammonia (CO,HO and NH); and this food it derives wholly from the atmosphere. Thus the whole vegetable kingdom is derived from the air. But since animals make no organic matter for themselves, but take it ready made from plants, they also derive the whole of their substance, indirectly through plants, from the air. Thus the whole organic kingdom is derived wholly from the air. In the decomposition of animal and vegetable matter, everywhere (general decay), the whole of this matter is again returned, in its original form, CO,HO and NH2, to the air. Thus the whole organic kingdom, including both vegetables and animals, may be regarded as so much matter forcibly taken, as it were, against law, from the atmosphere, embodied in concrete visible form-incarnated a little while on this our lower earth-only to be again returned to its native air; so much matter snatched from the domain of chemistry, retained with difficulty a little while in living forms-only a little while, for chemistry will claim her own-to be again returned to the domain of chemistry; so much matter raised as it were by great effort to a dizzy height, there balanced a little while as on a slender pinnacle, in a state of unstable equilibrium, again to rush headlong downwards to the lower plane to which it naturally belongs. Thus, one generation takes matter from the air, embodies it awhile in living forms, and in death again returns it to the air; another generation takes the same matter, embodies and again returns it-and so on forever, each generation rising, phoenix-like, from the ashes of the preceding. Thus the same identical matter has been embodied and disembodied, again embodied and disembodied, in perpetually recurring cycles; has been worked over and over again by an eternal circulation, thousands, yea, millions of times, from the very commencement of life upon this earth, through the countless ages of geology, even to the present time. It seems simple enough, nothing but the circulation of carbon, hydrogen, oxygen and nitrogenan eternal circulation driven by the sun; only in the course of this circulation certain wonderful phenomena of vegetable, animal and even intellectual life take place.

I might go further, if time permitted, and give reasons for believing that, as organic matter is only transformed-individualized mineral matter, so also organic force is only transformed-individualized chemical

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