almost sufficient to stun the observer, while I had two currents, or winds, sliding over each the snowflakes descend so softly as not to hurt the fragile spangles of which they are composed; yet to produce, from aqueous vapor, a quantity of that tender material which a child could carry demands an exertion of energy competent to gather up the shattered blocks of the largest stone-avalanche that I have ever seen and pitch them to twice the height from which they fell. WINDS. other and moving in opposite directions. Thus also, as regards our hemisphere, a current from the equator sets in toward the north and flows in the higher regions of the atmosphere, while. to supply its place, another flows toward the equator in the lower regions. These are the upper and the lower trade winds. Were the earth motionless, these two currents would run directly north and south, but the earth rotates from west to east on its axis once in twenty-four hours. In virtue of this rotation the air at the equator is carried round with a velocity of one thousand miles an hour. As we withdraw from the equator the velocity due to the earth's rotation diminishes, and it becomes nothing at the poles. It is portional to the radius of the parallels of latitude, and diminishes as these circles diminish in size. You have observed what takes place when a person incautiously steps out of a carriage in motion. He shares the motion. of the carriage, and when his feet touch the pro From the heat of the sun our winds are all derived. We live at the bottom of an aerial ocean in a remarkable degree permeable to the solar rays and but little disturbed by their direct action. But those rays, when they fall upon the earth, heat its surface, and when they fall upon the ocean they provoke evaporation. The air in contact with the surface shares its heat, is expanded and ascends into the upper regions of the atmosphere, while the vapor from the ocean also ascends, because of its lightness, carry-earth he is thrown forward in the direction ing air along with it. Where the rays fall vertically on the earth-that is to say, between the tropics-the heating of the surface is greatest. Here aërial currents ascend and flow laterally, north and south, toward the poles, the heavier air of the polar regions streaming in to supply the place vacated by the light and warm air. Thus we have incessant circulation. In the hot room of a Turkish bath I held a lighted taper in the open doorway, midway between top and bottom. The flame rose vertically from the taper. When placed at the bottom, the flame was blown. violently inward; when placed at the top, it was blown violently outward. Here we an of the motion. This is what renders leaping from a railway carriage, when the train is at full speed, generally fatal. Imagine, then, individual suddenly transferred from the equator to a place where the velocity due to rotation is only nine hundred miles an hour; on touching the earth he would be thrown forward in an easterly direction with a velocity of one hundred miles an hour, this being the difference between the equatorial velocity with which he started and the velocity of the earth's surface in his new locality. WARMTH OF CLOTHES. It is the imperfect conductivity of woollen textures which renders them so eminently fit for clothing. They preserve the body from sudden accessions and from sudden losses of heat. The same quality of non-conductivity manifests itself when we wrap flannel round a block of ice the ice thus preserved is not easily melted. In the case of the human body, on a cold day, the woollen clothing prevents the transmission of motion from within outward; in the case of the ice, on a warm day, the selfsame fabric prevents the transmission of motion from without inward. Animals which inhabit cold climates are furnished by Nature with their necessary clothing. Birds, especially, need this protection, for they are still more warm-blooded than the Mammalia. They are furnished with feathers, and between the feathers the interstices are filled with down, the molecular constitution and mechanical texture of which render it, perhaps, the worst of all conductors. Here we have another example of that harmonious relation of life to the conditions of life which is incessantly presented to the student of natural science. ENERGIES OF PLANTS AND ANIMALS. The farther we pursue this subject, the more its interest and its wonder grow upon us. You have learned how a sun may be produced by the mere exercise of gravitating force that by the collision of cold, dark planetary masses the light and heat of our central orb, and also of the fixed stars, may be obtained. But here we find the physical powers derived or derivable from the action of gravity upon dead matter introducing themselves at the very root of the question of vitality. We find in solar light and heat the very mainspring of vegetable life. But is there nothing in the human body to liberate it from that chain of necessity which the law of conservation coils around inorganic nature? Look at two men upon a mountainside with apparently equal physical strength; the one will sink and fail, while the other scales the summit. Has not volition, in this case, a creative power? Physically considered, the law that rules the operations of a steam-engine rules the operations of the climber. For every pound raised by the former an equivalent quantity of its heat disappears, and for every step the climber ascends an amount of heat equivalent jointly to his own weight and the height to which it is raised is lost to his body The strong will can draw largely upon the physical energy furnished by the food, but it can create nothing. The function of the will is to apply and direct, not to create. The grand point permanent throughout all these considerations is that nothing new is created in physical nature. We can make no movement which is not accounted for by the contemporaneous extinction of some other movement. And how complicated soever the motions of animals may be, whatever may be the change which the molecules of our food undergo within our bodies, the whole energy of animal life consists in the falling of the atoms of carbon and hydrogen and nitrogen from the high level which they occupy in the food to the low level which they occupy when they quit the body. But what has enabled the carbon and the hydrogen to fall? What first raised them to the level which rendered the fall possible? It is the sun. Not only is the sun chilled that we may have our external fires, but he is likewise chilled that we may have our internal warmth and our powers of locomotion. bining energy acts. In one case the germ determines the formation of a man; in another, the formation of a frog. All the philosophy of the present day tends to show that it is the directing and compounding, in the organic world, of forces belonging equally to the inorganic, that constitute the mystery and the miracle of vitality. In discussing the material combinations which result in the formation of the human organism, it is impossible to avoid taking side glances at the phenomena of The subject is of such vast importance, and is so sure to tinge the whole future course of philosophic thought, that I will dwell upon it a little longer, and endeavor, by reference to analogical processes, to give you a clearer idea of the part played by the sun in vital actions. We can raise water by mechanical action to a high level, and that water, in descending by its own gravity, may be made to assume a variety of forms and to perform various kinds of mechanical work. It may be made to fall in cascades, rise in fountains, twirl in eddies or flow along a uni-sciousness and thought. Science has asked form bed. It may, moreover, be employed to turn wheels, lift hammers, grind corn or drive piles. But all the energy exhibited by the water during its descent is merely the parcelling out and distribution of the original energy which raised it up on high. In this precise sense is the energy of man and animals the parcelling out and distribution of an energy originally exerted by the sun. But the question is not yet exhausted. Water produces all the motion displayed in its descent, but the form of the motion depends on the character of the machinery interposed in the path of the water. Thus also the primary action of the sun's rays is qualified by the atoms and molecules among which their power is distributed. Molecular forces determine the form which the solar energy will assume. In the one case this energy is so conditioned by its atomic machinery as to result in the formation of a cabbage; in another case it results in the formation of an oak. So, also, as regards the reunion of the carbon and the oxygen in the animal, the form of their reunion is determined by the molecular machinery through which the com daring questions, and will, no doubt, continue to ask such. Problems will assuredly present themselves to men of a future age which, if enunciated now, would appear to most people as the direct offspring of insanity. Still, though the progress and development of science may seem to be unlimited, there is a region beyond her reach-a line with which she does not even tend to inosculate. Given the masses and distances of the planets, we can infer the perturbations consequent on their mutual attractions; given the nature of a disturbance in water, air or ether, we can infer from the properties of the medium how its particles will be affected. In all this we deal with physical laws, and the mind runs freely along the line which connects the phenomena from beginning to end. But when we endeavor to pass, by a similar process, from the region of physics to that of thought, we meet a problem not only beyond our present powers, but transcending any conceivable expansion of the powers we now possess. We may think over the subject again and again, but it eludes all intellectual presentation. The origin of the material universe is equally inscrutable. Thus, having exhausted science and reached its very rim, the real mystery of existence still looms around us. And thus it will ever loom-ever beyond the bourne of man's intellect-giving the poets of successive ages just occasion to declare that "We are such stuff As dreams are made of, and our little life Still, presented rightly to the mind, the infringement of the law which reveals immutability in the midst of change, which recognizes incessant transference or conversion, but neither final gain nor loss. The energy of Nature is a constant quantity, and the utmost man can do in the pursuit of physical truth or in the applications of physical knowledge is to shift the constituents of the never-varying total, sacrificing one if he would produce another. The law of conservation rigidly excludes both creation and annihilation. Waves may change to ripples, and ripples to waves; magnitude may be substituted for number, and number for magnitude; asteroids may aggregate to suns, suns may invest their energy in flora and faunæ, and flora and fauna may melt in air: the flux of power is eternally the same. It rolls in music through the ages, while the manifestations of physical life, as well as the display of physical phenomena, are but the modulations of its rhythm. PROFESSOR JOHN TYNDALL. BY PRAYER. withstan ling this enormous drain, in the lapse MORE things are wrought by prayer of human history, we are unable to detect a diminution of his store. Measured by our Measured by our largest terrestrial standards, such a reservoir of power is infinite; but it is our privilege to rise above these standards, and to regard the sun himself as a speck in infinite extensiona mere drop in the universal sea. We analyze the space in which he is immersed and which is the vehicle of his power. We pass to other systems and other suns, each pouring forth energy like our own, but still without Than this world dreams of. Wherefore let thy voice Rise like a fountain for me night and day; prayer Both for themselves and those who call For so the whole round earth is every way ALFRED TENNYSON. One night, before the sheaves were gathered in, As Zimri lay upon his lonely bed So he arose and girded up his loins, Down to the field and add to his from And went down softly to the level field. The trees stood black against the cold blue Passed down the mountain-path and found sky, the field, The branches waved and whispered in the Took from his store of sheaves a generous wind; So Zimri, guided by the shifting light, the field, third And added them unto his brother's heap; Then he went back to sleep and happy dreams. |