Curiosities of Heat Part 14

"Will you not tell us," said Samuel, "how these ocean currents are produced? I can understand how winds are formed, but I do not see that these streams in the sea could be formed in the same way."

"I designed to speak of this, but for the moment it had slipped from my mind: I am glad that you called my attention to it. I do not expect, however, to give a full and satisfactory account of their origin. If I should do this, I should succeed where every other man has failed. I shall not attempt a full explanation. By some means or other, the waters of the ocean are thrown out of equilibrium, and these currents are plainly an effort to restore the balance or equilibrium of the waters. Many influences and agencies conspire to disturb the equilibrium of the sea.

The attractions of the sun and moon are constantly counteracting the attraction of the earth and lifting the waters, so to speak, above their natural level. The tides produced by these attractions of the sun and moon are the immediate cause of some of the minor local currents. The winds set the waters in motion, tending to pile them up in one place and leave the sea below its natural level at another. The effect of strong winds in piling up the waters, even upon our great lakes, is very considerable. A heavy east wind upon Lake Erie has been known to drive the waters toward the western end of the lake so much as to leave Niagara River above the falls almost dry. On the other hand, a heavy west wind drives the waters eastward, and produces almost a flood in the river. The influence of constant winds like the 'trades' acting upon an immense expanse of water must be very much greater. Unequal evaporation tends to destroy the balance of the waters. In the colder regions the evaporation is very little, while within the tropics it amounts to about half an inch daily, or fifteen feet per annum. The head of the Red Sea is two feet lower than its mouth on account of evaporation. This unequal evaporation causes also an unequal saltness, and consequently an unequal weight. The fresher and lighter water cannot balance an equal bulk of salter and heavier water.

When once currents are started the revolution of the earth upon its axis would affect them, just as the rotation of the earth affects the trade-winds. Now, all these various agencies, and perhaps many others, combine their influence to destroy the equilibrium of the waters of the ocean. They unite and interweave their influence in a thousand ways beyond all human calculation. The result is the ocean currents. But how much is due to one cause and how much to another in the present state of knowledge no man can tell. Only for a few years have the phenomena of ocean currents been made the object of scientific observation and research. But the effect of ocean currents in modifying climate is well understood, and the modification of climate means nothing else than the transfer of heat. This is all that I have to say of the rivers of the sea, and if there are no more questions, we will now look at the movement of heat caused by icebergs."

No question was asked, and Mr. Wilton continued:

"In polar regions there must be an immense formation of ice. Except in the oceans, the movements of water are chiefly movements of water in the condition of ice. Only for a small part of the year could water exist unfrozen. Immense regions of the Antarctic continent seem to be covered with one broad glacier. The ice pushes down into the sea until, undermined by the das.h.i.+ng of the waves, it breaks off, and enormous fragments are launched upon the deep waters. Sir James Ross saw in the southern ocean a chain of such icebergs extending as far as the eye could reach from the mast-head, many of them from one hundred feet to one hundred and eighty feet in height and miles across. Captain d'Urville saw one thirteen miles long and one hundred feet high. Its bulk was so vast that though the waves were das.h.i.+ng against it not a tremor was perceptible. Astronomic observations could be made from it as if it were solid rock rooted in the heart of the earth. In the same manner icebergs are formed in the northern ocean also. How much heat is given out in the freezing of water?"

"About one hundred and forty degrees," answered Peter.

"In the formation of icebergs, then, heat is given out nearly sufficient to boil an equal quant.i.ty of cold water. The icebergs float away toward the equator. They come down from Baffin's Bay till they meet the Gulf Stream off Newfoundland. In the southern hemisphere they come ten degrees nearer the equator. As they float toward the tropics they slowly melt, and in their melting they exact from the air and the sea where they melt the same amount of heat which they gave up in their freezing. If they melted at the same place where they froze, there would be no transfer of heat.

But they are formed in the polar regions; they give out their heat in the frigid zone, while they melt and absorb a like amount of heat from the temperate zones. In this manner the polar regions are exchanging with the temperate zones ice for water. They borrow water, rob it of its latent heat, and send it back in the form of ice. The temperate zones supply the needed heat and bring the ice back to the form of water, when the polar regions again borrow it, seize upon its heat, and again send it back in the form of ice mountains. The effect is the same as if thousands of railroad trains were transporting water to the frigid zones, leaving it there to freeze and give up its one hundred and forty degrees of latent heat, and bringing it back in the form of ice. Let us estimate the bulk of one such iceberg as that seen by Captain d'Urville. It was thirteen miles long and one hundred feet high, and we will suppose that it was four miles broad. Standing out from the water one hundred feet, it must have sunk at least eight hundred feet below the surface. This would give us the enormous bulk of (1,304,709,120,000) one trillion three hundred and four billions seven hundred and nine millions one hundred and twenty thousand cubic feet of ice. The burning of one pound of coal will generate heat sufficient to melt about five and a half cubic feet of ice. To melt one such iceberg would require more than one hundred and eighteen millions of tons of anthracite coal. This is the amount of heat given out in the polar region by its freezing. This is the amount of heat transported from the warmer to the colder regions. But what is one iceberg to the thousands which drift yearly from the frigid zones toward the tropics?

"But even this hardly represents the entire transfer of heat by the agency of icebergs. The icebergs are formed from the snows of polar storms, and these are formed from the condensation and freezing of vapors. In the process of condensation one thousand degrees of heat are given out. Every iceberg _represents_ a transfer of heat sufficient to boil more than six times its weight of ice water.

"One marked ill.u.s.tration of the effect of icebergs we ought to notice.

Down through Baffin's Bay icebergs are constantly floating. They are borne on southward till, in the still waters of the Grand Banks, between the polar current and the Gulf Stream, they float around and melt and disappear. To these melting icebergs the chilliness and unfailing fogs of the Grand Banks are due; and not only this, but the very existence of the Banks is supposed to be due to the deposit of sediment, sand, earth, and stone brought by polar ice.

"I have spoken only of the polar glaciers and the icebergs formed by their pus.h.i.+ng off into the sea. But the same transfer of heat is taking place, on a very much smaller scale and within narrow limits, by the glaciers of the Alps and every other mountain glacier. The glaciers are nothing else than rivers of ice. Snow falls upon the mountain tops and valleys of the mountain sides from age to age. The snow slowly changes to the structure of ice, and by its enormous weight flows down through the gorges of the mountain sides, till in the warmer vales below it melts and disappears.

We have not time to go into a full examination of all the interesting phenomena of glaciers, but this one point you will notice and remember: these rivers of ice--for they flow like rivers--cool the valleys and tend to warm the mountain tops; of course upon the tops of the mountains there can be no acc.u.mulation of heat, because, standing out into the eternal coldness of s.p.a.ce, and swept by winds for ever, and exposed by the thinness of the air to a rapidity of evaporation unknown at the sea level, heat is caught up and borne away in a moment.

[Ill.u.s.tration: TRANSPORTATION of HEAT.

Page 288.]

"This closes this department of our theme. I might have gone much more into details and given you great stores of particular facts and figures, but they would have added nothing to your understanding of the subject, and we can hardly afford to devote our Lord's Day to mastering the details of the natural sciences. We have now looked at some of the methods by which the extremes of heat and cold, in day and night, in summer and winter, and in the tropics and polar regions, are mitigated. The same principles operate upon the smallest and upon the largest scale. If there is need for me to attempt in a formal way to awaken in you admiration for the wisdom and goodness of G.o.d shown in all these beneficent arrangements for equalizing temperature, our study has been largely in vain. We have only to remember that all these contrivances are the Lord's designs. He created the world; he endowed matter with its qualities and forces, and he gave it these qualities and forces for the purpose of using it as he has used it. He planned all those contrivances by which he secures the comfort and the good of man, and the fact that these natural agencies are fitted for moral uses in recovering sinners to holiness and blessedness is but the culmination of its adaptation to the uses of man.

"This, however, does not complete our course of study. A few other points will demand our attention for two or three more lessons. But while we go on with our studies of Nature, remember that the physical was created for the sake of the spiritual; the spiritual is more important. Let us not subvert the divine order and sink the high purpose of the creation to mere material agencies and contrivances. To know G.o.d is greater and better than to understand Nature. That we might know and enjoy and glorify the Creator was the object of our creation. We cannot express it in better language than that employed in the old catechism: 'The chief end of man is to glorify G.o.d and enjoy him for ever.' That term 'for ever' includes the present life as well as the future. We ought to know, enjoy, and glorify G.o.d to-day. I hope that another week may find Ansel with some happy experience in this matter."

CHAPTER XIV.

COMBUSTION.--COAL-BEDS.

Another Lord's Day comes, and no change has taken place with the cla.s.s which calls for mention. Ansel still walks in darkness, ready indeed on every occasion to manifest his concern for the salvation of his soul, diligent in reading the Scriptures, frequent in prayer, and giving yet no indication of a flagging of his avowed purpose to follow Christ, but he receives no comfort and peace. A painful and distressed interest is becoming more and more concentrated upon him. What will be the end of his groping in darkness? This cannot last always. Unless the hindrance, whatever it be, which prevents the exercise of faith, be seen and removed, Ansel will probably soon go back to his former careless state, and, it may be, become tenfold more obdurate than before. He will be likely, on the one hand, to become self-righteous from his supposed effort to come to Jesus, and, on the other, discouraged and despairing, feeling that for him effort is vain and salvation unattainable. While he remains in this state the very lapse of time is dangerous. All feel concerned for him, but no questions are asked, and the lesson goes on as usual.

"The method of transferring heat which we are now to examine is wholly different in principle from any which we have as yet considered. I refer to the production of heat by combustion. The transfer of heat by combustion cannot be compared for vastness with those great movements of heat which have before claimed our attention, yet for the comfort and well-being of the human race combustion is exceedingly important. Without that command of heat which combustion gives, man could not rise at best above the savage state, and in fact could hardly exist upon the earth. We smile at the Grecian myth that Prometheus stole fire from the G.o.ds and brought it to men in his reed staff, but fire is certainly worthy of being counted one of G.o.d's great gifts. But whence comes the heat of combustion?

Is it a new and original generation of heat, or is it merely a transfer?

Will some one explain this?"

"I don't think that I can tell," said Samuel. "I remember the principles you have given us about the nature and production of heat, but I do not know how to apply them to combustion."

"I did not suppose that you would be able to explain all the phenomena of Nature at sight, yet the production of heat by combustion is not difficult to be understood. The burning of wood and coal is chiefly the union of oxygen with carbon. The oxygen of the air unites with the carbon of the combustible. The attractive force between oxygen and carbon is very strong. When they unite, the atoms of oxygen dash against the atoms of carbon with great violence. As they dash one upon another their motion is lost, but by the laws of trans.m.u.tation of forces that lost motion reappears as heat; that is, the motion of the atoms as they fall the one against the other is changed to that vibration of the atoms which we call heat. The atoms of carbon, in their separation from oxygen, may be compared to weights suspended, ready to fall. Let once the cord be cut, and the weight falls and dashes against the earth; its motion in falling is lost, and reappears as heat. So carbon is suspended, so to speak, waiting to unite with oxygen. But how is the weight raised? How is carbon brought into this state of suspense, waiting to dash upon oxygen and develop heat? That is not its natural state.

"Carbonic acid is found everywhere mingled in small proportions with the atmosphere. This carbonic acid is nothing else than carbon and oxygen united in the proportion of one atom of carbon to two atoms of oxygen.

This is the natural state of carbon. This carbonic acid is the food of plants; it is this which supports all vegetable growth. The carbonic acid is absorbed by the leaves of plants and trees, and in the hidden laboratory of the leaf, by what process is one of the undiscovered secrets of Nature, the carbon is separated from the oxygen, the oxygen is discharged through the pores of the leaf, and the carbon is carried into the circulation to build up the fabric of the woody fibre. That which the most skillful chemist in the world cannot do, except by indirect processes and at a high temperature, the leaves are doing directly at the ordinary temperature. Vegetable growth is a deoxidizing process. To accomplish this an enormous force is requisite. To separate carbon and oxygen, a force is demanded which is able to overcome their powerful attraction. How shall we estimate the strength of this force? In order that they may unite, as in the explosion of gunpowder, solid rocks are torn asunder. The attraction of carbon and oxygen is strong enough to tear great rocks in twain. It is this attraction which sends the cannon ball and the sh.e.l.l like meteors of death upon their errands of destruction. This great force must be overcome; carbon must be separated from oxygen and built into trees. This is the lifting up of the weight. But whence comes the force necessary to accomplish this? From the sunbeam. The heat of the summer's sun, employed as force, is used to deoxidize carbonic acid. Heat is used, and used up, in lifting the weight which in its fall shall generate again a like amount of heat. The combustion of wood produces the same amount of heat as was needful to separate its carbon from the carbonic acid of the air.

Vegetable growth is thus a cooling process; heat is withdrawn from use as heat, and is employed as force. As force it has nothing to do with temperature. The summer's heat, employed in vegetable growth, reappears in the blazing billets of the kitchen fire. Heat is condensed and solidified, so to speak, and placed under man's control. In this solidified form heat may be laid up in store or transported at pleasure.

"The grandest application of this principle is seen in the formation of the coal-beds. At some early period in the unmeasured ages past, the temperature of the earth must have been much higher than it now is; the air was filled with moisture, and carbonic acid abounded. As a consequence, there was an enormous vegetable growth. This, as we have seen, is a heat-consuming process. The heat is withdrawn from the air and employed in deoxidizing the carbonic acid. This vast vegetable growth--enormous ferns and coniferous trees--fell, and was swept by rivers or by floods into valleys, or the beds of lakes, or the sea; the sediment of the waters covered it, and there, shut up from the air and subjected to a heavy pressure, this vegetable ma.s.s underwent a slow transformation.

Peter, have you ever seen a coal-pit? I do not mean a coal _mine_, but that which charcoal-burners call a coal-pit."

"I have seen them many a time."

"Tell us, then, how wood is burned to coal without being burned up."

"The wood is set on end, closely packed in the shape of a mound, and then covered with earth. Fire is kindled in the middle of the pile, and just enough air admitted through air-holes at the bottom to keep up a slow burning. It burns just fast enough to heat and dry the wood without burning it up."

"The same process," said Mr. Wilton, "went on in the formation of the coal-beds, but very much more slowly. Under the pressure of earth and water the vegetable deposits lie smouldering, not for a few days, but probably for ages, till nothing but the carbon remains, and that pressed into a solid ma.s.s heavy as stone. Veins of coal are found interspersed with layers of earth and rock, layer above layer, and these layers are commonly not level, but more or less inclined and sometimes broken. This shows that a deposit of driftwood was made, then a deposit of sand or clay, then another deposit of vegetable material and another layer of earth. At length, by internal convulsions, the whole surface was raised from beneath the waters, and in due time the coal-veins were laid open, and the coal brought out for the use of man. Then the force so long pent up and held in suspense is set free; the stored-up heat of the geologic ages is brought out for use. The excess of heat in that ancient period is handed down to these later times. How sublime this transfer of heat! It carries us back, in imagination, to the 'heroic ages,' so to speak, of the history of creation. By other methods heat is treasured up for a day or a year: by this method it is kept in store for myriads of ages. We see that the same natural forces were working in those early ages as to-day, and the same benevolent Creator was arranging the affairs of the world for man's advantage. The sunbeam which streamed upon the earth long ages before man was created is to-day smelting ores, driving machinery, dragging ponderous trains of loaded cars, and ploughing the seas with freighted keels. This seems like a fairy-story or a dream, but instead of that it is the soberest of philosophic and scientific truth.

"We ought also to notice the internal heat of the earth. This has been handed down from the day of creation, it would seem, till the present. No new principle is seen in the earth's internal fires, but a sublime ill.u.s.tration of the storing up of heat in a hot body and its slow radiation.

"The origin of the internal heat of the earth we can only conjecture.

Perhaps G.o.d created the various elements separate, uncombined, and allowed them then to combine according to their natural affinities. This sublime conflagration of all the elements of the earth would generate the highest temperature which could be produced by combustion. The elements would melt with fervent heat; everything which could be vaporized by heat would be turned to vapor. Then radiation of heat would begin. Vapors would sink to fluids and fluids turn to solids; a hard crust would be formed on the surface of the globe through which the heat of the still molten ma.s.s within would be slowly conducted and escape. Upon this internal heat the earth depends in no small degree for its temperature. The heat generated perhaps upon the day of creation helps now to render the earth habitable.

"That the earth was once in a fluid state and has lost a portion of its heat by radiation is indicated by several facts. It is one of the received beliefs among geologists that at some period in the past the temperature of the earth was much higher than it now is. The animals and plants which flourished during the ages when the coal-fields were deposited show that sea and land were warmer than at present. It is believed that the change of temperature has taken place on account of the cooling of the earth from radiation. The rate of radiation is so slow, however, that no farther sensible change of temperature can take place for thousands of generations.

"The form of the earth also indicates that it was once fluid. The earth is an oblate spheroid, a flattened sphere, and has that degree of flatness which a fluid ma.s.s would a.s.sume if revolving at its present rate. The earth swells at the equator and rises thirteen or fourteen miles above the sea level at the poles. The waters of the ocean move freely and take the same form as if the whole globe were fluid, and the solid parts of the earth have the same degree of convexity, which shows that it took its form from its own rotation upon its axis while in a fluid state. This would also show that in the primal ages, when the earth was in a plastic or fluid state, it had the same rate of rotation as at present.

"The lifting up of the mountain ranges also is best explained by supposing that the earth was once molten. The earth cooled, a crust was formed, and by farther cooling and contraction of the molten ma.s.s within the crust wrinkled and formed mountain chains. Thus the higher temperature of the geologic ages, the form of the earth as if it were a revolving fluid ma.s.s, and the corrugation of its surface--these, joined with its present internal heat, point to the fact that it was once molten and fluid to its surface. The benefits of this heat laid up in store on the day of creation we still enjoy."

"Before the cla.s.s is dismissed," said Mr. Hume, "I should like to say a few words."

"I have nothing farther to say to-day," answered Mr. Wilton, "and we should be glad to hear you now. Say on."

"I wish only to say that these lessons have led me to such thoughts of G.o.d's wisdom and goodness as I never had before. Of course it is not strange that this should be the case with me. I now look at everything with new eyes. It is not merely this one element of heat in Nature that moves my admiration, but I have been led to consider a thousand things in which the goodness of G.o.d is shown. My thoughts of the divine goodness are as fresh and interesting to me as my impressions of his righteousness and holiness are startling. For years I have tried with might and main to look upon the dark side of the world and to exaggerate its physical evils.

I have searched for disorder and want of adaptation. As long as I misunderstood the purpose of the creation, I thought I was successful in impugning the wisdom of the arrangements of this physical world. While I supposed that the earth must needs be the Creator's masterpiece in beauty and pleasantness and all manner of perfections, designed just to give sensual pleasure to its inhabitants, I could find, or thought I found, many faults in the Creator's work. Now I withdraw all my former charges.

My eyes are opened. The rougher elements of man's life will henceforth have a new meaning to me. I see that G.o.d seeks not so much present pleasure for men as their holiness. He lays a solid foundation for their happiness. He seeks to render men blessed by bringing them into likeness and union with himself. These are new views to me, and I thank my heavenly Father that this new light has dawned upon me. I feel now that I can bear the ills of this life cheerfully, understanding that the Lord is using them as a means of spiritual discipline. It seems to me as if this lower world and man's lowly life were already glorified by a beam of light falling from heaven. I hope that my young friends have been as much profited as I have been."

"I rejoice with you, Mr. Hume. 'We know that all things work together for good to them that love G.o.d.' This light has shone upon me for many years."

CHAPTER XV.

ECONOMY OF HEAT.

"In this final lesson I wish," said Mr. Wilton, "to bring before you some general views of the whole subject of the agency and management of heat.

"When Jesus had fed the five thousand men upon the mountain side by the Sea of Galilee, he said to his disciples, 'Gather up the fragments that remain, that nothing be lost.' The Christ who spoke these words was the same Christ by whom 'all things were created that are in heaven and that are in the earth, visible and invisible.' These words inculcate the propriety of saving, the very opposite of extravagance and wastefulness.

The same prudent economy we find in all G.o.d's works. Nothing is wasted.

G.o.d provides bountifully; he is not stinted in his works; we find nothing narrow or mean; his resources are ample for all his undertakings. Perhaps a careless observer might charge him with prodigality and wastefulness.