Solar heat

“ For this reason astronomers generally, while conceding that a portion, and possibly a considerable fraction, of the solar heat may be accounted for by this hypothesis, are disposed to look further for their explanation of the principal revenue of solar energy. They find it in the probable slow contraction of the sun's diameter, and the gradual liquefaction and solidification of the gaseous mass. The same total amount of heat is produced when a body moves against a resistance which brings it to rest gradually, as if it had fallen through the same distance freely and been suddenly stopped. ”

“ Effect of Solar Heat on the Earth.—That the sun’s heat passes into the interior of the earth in a variable manner, depending upon the succession of days and nights, summers and winters, is an obvious consequence of our first notions on this subject. The mode in which it proceeds into the interior, after descending below the surface, remained to be gathered, either from the phenomena, or from reasoning. ”

“ Although I can not pretend to an intimate acquaintance with the more intricate phenomena of solar physics, I have long had a conviction, derived principally from familiarity with some of the terrestrial effects of heat, that the prodigious dissipation of solar heat is unnecessary to satisfy accepted principles regarding the conservation of energy, but that solar heat may be arrested and returned over and over again to the sun, in a manner somewhat analogous to the action of the heat recuperator in the regenerative engine and gas-furnace. ”

“ Does the planet radiate heat of the wave-lengths that it receives from the sun? and how is its temperature maintained, probably several hundred degrees above the temperature of space, when our observations show that the direct radiations of heat from the sun can only raise it about fifty degrees above the surrounding temperature? Experiments at Allegheny show that the dark solar heat is transmitted by our atmosphere with less difficulty than the light ”

“ Yet it is difficult to see how, on any hypothesis of the generation of solar heat, or by combining together all possible modes of heat generation, a supply for more than twenty millions of years in the past and a possible supply for as long a period in the future can be accounted for. ”

“ The action of the absorbed heat in reference to cloud-formation is directly opposite to that of the transmitted solar heat, as this reaching the surface of the earth evaporates the superficial water, and thereby produces the material of clouds. On the other hand, the heat which is absorbed by the air increases its vapor-holding capacity, and thus prevents the formation of clouds, or even effects the dissolution of clouds already formed. ”

“ The condensation of volume of the planets will give rise to great elevation of temperature, while their currents of electricity, poured into the sun, will, by their passage through its enormously compressed hydrogen atmosphere, produce intense heat, and this, rapidly communicated to the solar core within, will raise its temperature to that of the sun as we now see it, and permanently maintain it in that state of incandescence. ”

“ When we consider that the thickening of this solar atmosphere would bring back the age of ice, or its thinning carry our polar regions to tropical temperature, and when we remember that rhythmical action, not uniformity, seems to be the law of nature here, we can feel no certainty of the future constancy of the solar heat, nor of our protection against such changes as seem to have befallen other suns in space, and against which we are powerless to guard. ”

“ According to this view, the solar heat receives occasional accessions from the fall upon the sun's surface of masses of meteoric matter. There can be hardly a doubt that such masses do fall upon the sun; there is certainly no doubt that if they do, the sun must gain some heat thereby. ”

“ The mean value which has been arrived at is fourteen, and the fundamental fact with regard to the solar radiation which we are thus enabled to state is that an area of a square foot exposed at right angles to the solar rays, at a distance of 93 millions of miles, will in each minute receive from the sun as much heat as would raise one pound of water fourteen degrees Fahrenheit. ”

“ The solar heat, which grows for us the food by which we live, is no doubt in one sense the final cause of every meteorological change, bringing those years of want and years of plenty which are due to local variations of climate, that depend, through a chain of causes very remote and obscure, no doubt, yet finally, upon the sun. ”

“ Unless there exists in nature some process, of which we know nothing at present, whereby energy is renewed, our solar system must one day sink to this absolute zero of temperature. The sun, the earth, and every other body in the universe is steadily radiating heat, and this radiation cannot go on for ever, because heat continually tends to diffuse and to equalise temperatures. ”

“ By the unequal action of the solar heat are produced all winds and storms, and those disturbances in the electric equilibrium of the atmosphere which give rise to the phenomena of terrestrial magnetism. By the solar rays the waters of the sea are drawn up into the air in vapour, to descend again in rain, irrigating and fertilizing the land, and producing springs and rivers. ”

“ This being established, we may appeal to observation for proof that it is at the surface of the earth the greatest variations of temperature take place, and from this surface they are propagated upwards with diminishing force into the air above, and into the water and earth below, till in each direction they terminate, or become insensible. The communication of solar heat into the earth constitutes the first branch of our inquiry, and it has been quite sufficiently prosecuted to authorise the following positive statements. ”

“ As for directly storing up solar heat in good conductors or absorbents of heat which are then to be insulated—for instance, receiving the heat in porous black stones which are first exposed to the sun and afterward thrown into a great reservoir, just as snow is piled up in the ice-house—it involves no impossibility. ”

“ It is certain that the sun must under such circumstances fall some degrees in temperature each year. In a couple of thousand years the change in temperature would be sufficiently great to affect in the profoundest manner the supply of sunbeams. As, however, we know that for a couple of thousand years, or, indeed, for periods much longer still, there has been no perceptible decrease in the volume of solar radiations, we conclude that the great luminary cannot be regarded merely as a glowing solid globe dispensing its heat by radiation. ”

“ If the amount of solar light is enormous as compared with terrestrial standards, the same thing is still more true of the solar heat, which admits of somewhat more accurate measurement, since we are no longer dependent on a so unsatisfactory unit as the "candle-power," and can substitute thermometers and balances for the human eye. ”

“ The heat motion then disappears as heat by its conversion into work, just as the motion of a belt in a mill disappears in the work of the machine which it drives. One two-hundred-and-thirty-two-millionth part of the radiant solar energy, we know, is caught by the flying planets of our system in the forms of heat and light, adapted to sustain life and its continued [140] potentiality, and we know that this solar energy is the sole source of all the development and maintenance of the planets as the possible abodes of organic life, past, present or future. ”

“ This cause more sensibly affects places far removed from the equator, because at such places the days are longer and the nights shorter than in the torrid zone. By the operation of this cause, the solar heat accumulates there so much, during the longest days of Summer, that the temperature rises to a higher degree than is often known in the torrid climates. ”

“ And we are enabled, knowing the increasing rarity of the upper regions of our gaseous envelope, in which the absorption is constantly diminishing, to prove that about one-third of the solar heat is lost by vertical transmission through the whole extent of our atmosphere.—J. D. Forbes, F.R.S. ”

“ Condensation of the solar volume is unquestionably a source of heat, for we know that the solid or liquid interior of the earth increases in temperature at a definite ratio as we descend through its crust; but long before the sun shall have become contracted to the density of the earth all its heat will have become substantially internal heat, and it can then supply no more by radiation to its surrounding planets. ”

“ We see, therefore, that the direct rays of solar heat produce less effect upon the snow than those which are radiated from coloured surfaces. By numerous experiments, it has been shown that these secondary radiations are more abundantly absorbed by snow or white bodies than the direct solar rays themselves. Here is one of the many very curious evidences, which science lays open to us, of the intimate connection between the most ethereal and the grosser forms of matter. Heat, by touching the earth, becomes more earth-like. ”

“ How Heat and Light Reach the Earth. The heat of the sun is some forty-six thousand times as intense as is the heat of the earth. The violent agitations of the molecules of the sun’s hot atmosphere impart vibrations to the ether of space, which decrease in effectiveness inversely as the square of the distance; that is to say, that if the earth were twice as far from the sun as it is, the intensity of the solar rays would be one fourth of what they are now. These vibrations are called solar energy. They pass through space without perceptibly warming or lighting it. ”

“ Let us apply this principle to the solar system, and endeavour to find out whether in that system we have, in relation to the heat thereof, either a cycle of operations or a reversible cycle. We have again to consider the sun as the source of all light and heat in the solar [118] system, radiating forth on every side, year by year, the countless units of heat which go to form the continuance of all planetary life and existence. One of the problems that has confronted scientific men for many years is this, Where does the sun get its supply of heat from? ”

“ The sun seems to be a variable star, the variation in its heat and light is the natural consequence of the incessant changes of temperature and pressure, in the circulation, the electricity and magnetism, which are going on within the solar mass. We have already been able to show from our studies of the barometric pressure, temperature and vapor pressure in different parts of the earth, especially of the United States, that there is a definite though complicated synchronism, which connects the variations of the solar action with the variation in the terrestrial climatic effects. ”

“ Many attempts have been made in tropical and sub-tropical climates to utilize the sun's heat directly for power, and Ericsson in Sweden, Mouchot in France, and Shuman in Egypt have built successful and efficient solar engines. ”

“ It seems, therefore, most probable that we can not for the future reckon on more of solar radiation than, if so much as, twenty million times the amount at present radiated out in a year. It is also to be remarked that the greatly diminished radiating surface, at a much lower temperature, would give out annually much less heat than the sun in his present condition gives. ”

“ Through all these ages the sun must have been pouring out his radiant energy at at least his present rate. Radiation of heat from the earth may have been relatively less rapid from a denser carbon-laden atmosphere in times past than at present, but it never could have been more so. ”

“ In the meantime it must be observed, that there may be many operations of the solar rays, relating, too, to the nature of heat, which are not proportioned to our touch, so that, with regard to us, they do not tend to produce warmth, but, with regard to some other bodies, have their due effect in producing it.
Let the following experiment be made. Take a lens the reverse of a burning-glass, and place it between the hand and the solar rays, and observe whether it diminish the heat of the sun as a burning-glass increases it. ”

“ The great difficulty, that of the perpetual renewal of the solar fuel, still remains unsolved; the fact that during the millions of years of geological history we find no indications of any declining average of solar energy is so far still unexplained by this, as by every other, attempt to account for the origin of solar and stellar light and heat. ”

“ The sun is thus, in effect, a self-compensating machine, and its passage through a region of increased electrical generation would first manifest itself in a vast increase of brilliancy, due to higher incandescence of its hydrogen envelope; this, in turn, would be communicated to the deeper structures of the sun, producing increased volatilization [196] and dark absorption bands, and finally to the whole solar mass, expanding its volume in proportion to the heat absorbed. ”

“ It can be demonstrated that the conditions under which a mass of matter becomes so highly heated as to shine with star-like radiance are wholly exceptional in their character. So far as our present knowledge goes it would seem that the brightness of any sun-like body is to be attributed solely to the transformation in some fashion of mechanical power into heat. To take our own sun as an example, it is now an assured doctrine that the heat so necessary for our welfare is sustained by the gradual contraction of the solar volume. ”