"But remember, also, that G.o.d does not limit his expression of wrath to these natural agencies. The smile of G.o.d beams direct upon the soul as the warm rays of the sun fall upon the cold earth, and the frown of G.o.d throws a shadow which darkens the soul with the gloom of eternal death."

This discourse stirred the mind of Mr. Hume in a wonderful manner. The story of G.o.d's judgments upon wicked men and dissolute cities he had read many a time in his boyhood, but the rapid review of them by Mr. Wilton seemed to bring them up with a lifelike vividness. And that view of the forces of Nature, as allied with the moral laws of G.o.d to work out wrath upon evil-doers, was new to him, but his own mind quick as thought suggested many more ill.u.s.trations than Mr. Wilton had time to give. He remembered that all manner of vices--drunkenness, l.u.s.t, devotion to gay, sensual pleasures--bring ruin to men. He had noticed that the saddest faces are those of worn-out lovers of pleasure, and he knew that lovers of pleasure are very quickly worn out--that five years of sensuality will waste the powers of life more than fifty years of good work. He knew also that infidels and blasphemers, whatever else they might be, were unhappy men, and died joyless, foreboding deaths. He was not exactly angry, but his heart rebelled against thus being held by the mighty power of G.o.d, willing or unwilling, and against the thought that even Nature herself had conspired against him. It seemed to him hard that he was born into such a world, and that there was no escape from it. He did not consider at the moment that G.o.d and his works were against him only because he was against G.o.d, and that by submitting to G.o.d in loving obedience all the forces of G.o.d's world and G.o.d's providential government would turn in his favor--"that all things work together for good to them that love G.o.d."

At length better thoughts came to him. "I must know," he said to himself, "whether these things are so. I have never examined the subject to discover the truth, but have tried to find reasons for disbelieving the Bible and denying the gospel. I ought to look at the other side. If Nature and Nature's G.o.d have blessings in store for the willing and the obedient, why should not I know this and receive my share?"

Under the impulse of thoughts like these he formed the sudden resolution to join Mr. Wilton's Bible cla.s.s--that is, if he would receive him willingly, of which he had no small doubt. Coming directly forward at the proper time, he said to Mr. Wilton:

"I have learned what your cla.s.s is studying, and should like, I hardly know why, to join your cla.s.s for a few Sundays, if you are entirely willing."

Mr. Wilton, of course, did not know the exact state of Mr. Hume's mind; he did not know but that he came with a contentious spirit to bring up objections and propose hard questions; but he felt certain that, whatever his state of mind, the Spirit of G.o.d was bringing him to take this step.

He had prayed for him; in prayer his soul had travailed in pain for him; and he felt that by way of the throne of grace he had obtained a hold upon Mr. Hume--that the Holy Spirit had bound a cord between them which could not be broken. He believed, therefore, that, whether he came penitent or angry, good would result from his coming. He gave him, therefore, a hearty welcome.

"I am not only willing," he said, "but very glad, to have you come; and as I know that you have kept yourself informed of the latest phases of modern science, I hope we shall have your help in unfolding the subject which we are engaged in studying. I think you will be able to do us good."

"Your kind welcome ought certainly to incline me to do anything which I can to help the interest of your study, but I only ask the privilege of sitting with your cla.s.s as a silent listener."

The Sunday-school opened as usual, and the cla.s.ses entered upon their work.

"You have come in, Mr. Hume, at just the proper point in the progress of our lessons," said Mr. Wilton. "We have been preparing the way by a brief review of the laws of heat. We have gone over the effects of heat; the conduction, radiation, and convection of heat; thermal reflection, absorption, and transmission; specific and latent heat. We have tried to form a conception of the existence and operations of heat according to the dynamic theory that heat is a mode of atomic motion. This review would have had little interest to you. We are now prepared to look at the goodness and wisdom of G.o.d in the management of heat. We are not trying to prove the existence of a Creator and Governor--we are only looking at the mighty and wise works of that G.o.d in whom we already believe. We shall find the works of G.o.d planned and wrought out with wondrous skill, and that wonderful skill is employed in the interest of goodness. G.o.d has planned and wrought for the benefit of his creatures. His wisdom and goodness are exhibited on the grandest scale and in gigantic proportions.

This is all that is needed practically to demonstrate the existence of G.o.d. A good conscience does the rest. Being once a.s.sured that there is a Creator, a good conscience leaps to the conclusion that we ought to obey and serve him. Nay, the very work and existence of a conscience implies a divine Lawgiver and Ruler. To a good conscience a G.o.d is a necessity. But as we are not now attempting to show that there is a G.o.d, but to study his works, we will pa.s.s this point.

"With respect to the subject before us, let us first notice that heat is a necessity to the world and to man, and that G.o.d has made ample provision for that need. What the condition of the world would be without heat we can only conjecture. In the polar regions a natural temperature of seventy degrees below zero has been observed. At this temperature all the water upon the globe would turn to ice hard as adamant; all vegetation would cease, and with the disappearance of vegetable life all animal life must perish. The whole earth would be a frozen, lifeless, silent waste in the midst of silent s.p.a.ce. Some lines in Byron's picture of universal darkness would fitly describe the state of the world:

'The waves are dead, the tides are in their grave, The winds are withered in the stagnant air, And the clouds are perished.'

This description would be no figure, for motion as well as life depends upon heat. Yet seventy degrees below zero is but the beginning of cold.

'By mixing liquid protoxide of nitrogen with bisulphate of carbon in a vacuum, M. Natterer produced a temperature of two hundred and twenty degrees below zero.' At this temperature some of the so-called permanent gases--as carbonic acid, chlorine, and ammonia--can be compressed into liquids, and it is believed that in the complete absence of all heat all the gases would become solids. But by the agency of heat the world teems with active life. Vegetation clothes the earth with a garment of beauty; and earth, air, and sea swarm with living creatures full of enjoyment.

This great need of the world is bountifully supplied. The power and wisdom of G.o.d are employed in producing happiness.

"This, however, is but a part of the benefit which heat confers upon the world. The chief inhabitant of the earth is man, and man was created for something higher than bare existence. He was created for civilization and culture. The savage state is not, as some self-styled philosophers dream, the natural state of man. Nothing is so much against Nature. The natural state is that condition in which he attains the fullest development. Let a brute be placed in so unfavorable conditions that his growth is dwarfed and his natural instincts are not called into exercise, and no one would look upon that as a natural state. But man, wild, uncultured, undeveloped, is spoken of as being in his natural state. There could be no greater mistake. Culture and civilization are according to Nature, but culture and civilization require that man should get the mastery of Nature and subdue her forces. Till man gets the victory over the forces of this rough world, he spends a precarious existence in a hard struggle to gain a meagre support for his animal life. But when once science brings art, and the mastery of Nature is gained, man can rise into culture and beauty.

Opportunity is given for development. He blossoms into greatness and strength. Ideal and spiritual ends take the place of mere subsistence.

"But by what agency does man achieve the mastery of Nature? By the agency of heat. By the aid of heat man subdues the world. Heat brings the l.u.s.trous metal from its native ore; heat fashions the metal into a thousand shapes for the use of men; heat reigns as king in the curious processes of the chemist's laboratory, and the laboratory is the mother of all those modern arts which bless and beautify human life. By heat man prepares his food; by heat he drives his machinery; by heat he outstrips the flight of the winds; by heat he turns winter into summer and in his own dwelling makes for himself a perpetual springtime. For these purposes of human comfort and culture, G.o.d has provided generous stores of heat and placed them under man's control. He has placed in man's hands the means by which he can generate a heat which devours the hardest metals like stubble and a cold greater by far than Nature ever produces. We see that the Creator has provided for man as a being susceptible of culture and development, as a being of soul and sentiment, of spirit and aspiration.

G.o.d has fitted the world to be the dwelling-place of spiritual beings like man."

"I beg your pardon," said Mr. Hume at this point, "that the first word I speak in your cla.s.s should be a question which amounts to an objection."

"I shall be glad," said Mr. Wilton, "to hear your question, even though it be an objection. I will also answer it if I can."

"I wished to ask why it is, if G.o.d designed to provide for man's wants, that man can supply his wants, especially his higher wants--the wants of his intellectual and spiritual nature--only with the greatest difficulty and toil? The brutes supply their need with comparative ease, but man with boundless thought and labor."

"Your question is an important one, and deserves an answer. For myself, I look upon the fact to which you refer as one of the many points in which this world is adapted to human needs. Man is put in a condition which requires boundless thought and toil for the supply of his higher wants just because he possesses a n.o.bler nature and such thought and exertion are needed for its development. Which is the more desirable condition for a young man to be placed in--one in which his every wish is antic.i.p.ated and his every aspiration is gratified without exertion on his own part, or one in which opportunity and means are furnished for self-help, one in which he can supply his wants and satisfy his aspirations only by the exercise of his best abilities? Which will encourage the larger manliness and nurture the higher culture and strength? He who has no need for exertion rises at best only to a soft and feeble luxury, without mental vigor or moral force. What does man need besides scope and reward for exertion? Effort and struggle are necessities of our nature. This is especially true of man's higher faculties. Human greatness and goodness are not created by a word: they must be developed by exertion. For this reason G.o.d has made exertion necessary, and as much more necessary with man than with the brutes as his culture is more the result of voluntary, intelligent exertion. Does this explanation seem to you satisfactory, Mr.

Hume?"

"I have no fault to find with it; I must think of it."

"Very well, then; if no other one has a question to ask, we will look at another subject. We will survey the storehouses of heat which G.o.d has prepared for warming the earth. Samuel, you may name the first great source of heat."

"I think, sir, that the sun is the chief source of heat."

"We certainly receive the larger part of our heat from the sun. No one can doubt this. So much of our heat comes from the sun that the temperature of the earth varies according to the sun's heat, as if that were the only supply. If but a fleecy cloud pa.s.s between the sun and the earth, we feel a decided change of temperature. A few hours less of sunshine each day, and a few degrees more of inclination to the sun's rays, change summer to winter and make the difference between the torrid and the frigid zones.

Withdraw the heat of the sun altogether, and the whole world would become a desert of frozen death."

"What is the cause of the sun's heat?" asked Peter.

"You have asked a question which I cannot answer, and which no man can answer. The most careful and patient observations have been made to discover if possible the const.i.tution of the sun; learned and curious conjectures have been brought forward to explain the source of its heat; but the positive results have not been very large. It is certain that the sun is a globe revolving upon its axis in a period of twenty-five days, nine hours, and thirty-six minutes. This is known by the motion of dark spots upon its surface. The appearance of the sun as seen through a telescope is that of a globe of fire, its surface often in a state of violent agitation and flecked here and there with dark, irregular, changeable spots. These spots are sometimes of enormous dimensions--thirty thousand or fifty thousand miles in diameter. They present a dark centre with a narrow border or penumbra of lighter shade. To account for these spots, it has been conjectured that the body of the sun is dark, but surrounded by a double envelope of clouds, the outer layer of which is intensely luminous. Openings in such enveloping clouds would present an appearance like the spots upon the sun. According to this supposition, the heat and light of the sun proceed, not from the body of the sun, but from this luminous enveloping cloud. But granting that this supposition is true, it gives no explanation of the origin of the sun's heat. Laplace conjectured that the sun is a globe of fire in a state of violent, explosive conflagration, and that the spots are enormous crater-like caverns in its surface. Newton conjectured that comets falling into the sun and being consumed feed the solar fires and maintain its temperature.

The reception of the dynamic theory of heat has led to the revival, in a modified form, of this conjecture of Newton. It is suggested that meteors or meteoric matter falling into the sun generates its heat by the force of concussion. To show that the intense heat of the sun might be thus generated, elaborate calculations have been made. It has been demonstrated that if the sun were a solid ma.s.s of anthracite coal, its combustion would maintain its heat at its present rate of emission only five thousand years, while the falling of the planet Jupiter into the sun would generate an equal amount of heat for thirty-five thousand years. A lump of coal falling from the earth to the sun would produce three thousand times more heat by the concussion than by its combustion.

"The nearest approach that has been made, of an exact and scientific kind, toward determining the const.i.tution of the sun's surface has resulted from an examination of the _solar spectrum_. A ray of light, by pa.s.sing through a triangular prism of gla.s.s, is, as you know, divided into its elements, or const.i.tuent colors. The ray of light is spread out like a half-open fan. This divided and expanded ray, thrown upon a screen, is called the spectrum. An examination of the solar spectrum by a microscope shows certain fine dark lines across it. The lines are invariably the same in their position and grouping. The spectrum of the stellar light is found to differ from that of the solar light, and the light of one star differs from that of another star. Light from incandescent metallic vapors gives bright lines across the spectrum. Each metal has its own number, position, grouping, and color of these spectral lines. By comparing the solar spectrum with the spectra of the various metals--the processes are curious and the explanation difficult to be understood--corresponding lines are discovered, and the conclusion is reached that the sun's atmosphere contains the vapors of several of our well-known metals, as iron, nickel, sodium, pota.s.sium, and others. This is a most curious and marvelous scientific feat, to make an approximate chemical a.n.a.lysis of the sun and stars by means of their light. The conclusions, however, seem trustworthy.

"Can you tell us, Ansel, whether the earth receives heat from the moon and stars?"

"I cannot, sir."

"I should be glad, Mr. Hume, to have you instruct us upon this point."

"In regard to the fixed stars," answered Mr. Hume, "counting them as the remote suns of other planetary systems, we must believe that they radiate more or less heat upon the earth; some indeed have extravagantly maintained that we receive from them nearly as much heat as from the sun.

The heat received from them is so small that we perceive no difference whether they be hidden, or shine with their utmost brilliancy. I do not know that investigations have been made to determine scientifically their exact thermal influence upon the earth. But little more can be said about the heat of the moon. The light of the full moon, concentrated by a two-foot burning-gla.s.s and thrown upon the bulb of the most delicate thermometer, produces no perceptible effect. By means of the electroscope or galvanometer, it is said, however, that the moon's heat has been detected. At a late scientific convention held in Chicago, Prof. Elias Loomis read a paper, in which he stated that Mr. Harrison of England, by a comparison of observations made for sixteen years at Greenwich, nine years at Oxford, and sixteen years at Berlin, has discovered that the moon exerts a sensible influence upon the temperature of the earth, the highest temperature occurring from six to nine days after the new moon and the lowest about four days after the full moon. The conclusion, the opposite of what we should naturally expect--the higher temperature occurring when the enlightened face of the moon is turned from the earth--was explained by supposing the moon's heat to be dark heat which would be absorbed by the vapors and the clouds, and thus tend to warm and dissipate them. By the dispersion of the clouds, the radiation of heat from the earth's surface would go on more rapidly and the temperature would fall. According to this explanation, the lunar heat reduces instead of raising the temperature of the earth. The difference of temperature due to the moon's influence Mr. Harrison believed to be two and a half degrees. Upon extending his calculations through forty-three years of observations made at Greenwich, he found the difference reduced to about one degree. As for myself, I confess myself still a skeptic touching the supposed influence of the moon upon temperature."

"Upon that subject, I think," said Mr. Wilton, "that we must wait patiently for more light. The popular superst.i.tions which refer sickness and health, and every kind of good or evil fortune, to the benign or malignant influence of the moon, we, of course, must reject. Samuel, will you name the second chief source of heat?"

"I am obliged to answer as Ansel answered just now--I cannot tell. The enormous amount of wood and coal burned amounts to something, but this can have very little effect upon the temperature of the earth."

"The second great store of heat is the internal heat of the earth," said Mr. Wilton. "The importance of this store of heat we can easily understand by considering that the earth is a ma.s.s of molten mineral matter cooled and hardened upon the surface. The crust upon which we live is warmed from beneath by an ocean, or rather a globe, a world, of glowing molten rock.

Deep excavations have been made in mining operations, and artesian wells have been bored to still greater depths--as deep as two thousand, three thousand, or thirty-five hundred feet. The heat of the sun penetrates not more than seventy-five or a hundred feet; below that depth the temperature of the earth remains the same throughout the year. Below the point of constant temperature the heat of the earth is found to increase regularly and constantly. The rate of increase varies in different regions, but the average rate is about one degree of temperature for each fifty or sixty feet of descent. From this rate of increase it is easy to calculate the temperature at any given depth. At a depth of less than two miles water would boil. At twelve miles in depth the rock becomes incandescent. At twenty-two miles silver melts, at twenty-four miles gold melts, and at thirty-five miles cast iron becomes liquid. Volcanic eruptions also demonstrate the existence of immense ma.s.ses of molten rock in the interior of the earth; and we can account for the existence of volcanoes only by supposing that they now communicate or once communicated with the deep interior heat of the earth. The thickness of the earth's crust is, however, a matter of conjecture. The melting point of different substances rises as the pressure upon them increases, and as the density of the rock increases its conducting power becomes greater. The crust of the earth, therefore, may be fifty miles in thickness, or it may be one hundred miles or two hundred or three hundred miles. The effect of this internal heat in maintaining the temperature of the earth must be very great."

"I want to ask," said Peter, "how this internal heat came to exist, and how it is maintained?"

"This, like your former question, is altogether beyond our knowledge. All that we certainly know is that G.o.d made it thus. The process of creation, if indeed G.o.d did not create the earth by a word, without a process, is a matter of sublimest and most venturesome conjecture. According to the opinion of some, the elements of which the earth is composed were created separate and uncombined, and were suffered afterward to unite by their chemical affinities. This chemical combination would be nothing else than a tremendous conflagration, and the result would be the most intense heat of which we can form a conception. Others have dreamed of a 'fire-mist'

created of G.o.d and by some means condensed into worlds. The temperature of the earth is maintained, so far as we know, only by the poor conducting quality of the enveloping crust preventing its cooling. At the present rate of radiation, millions of years would be required to render the change of temperature perceptible.

"What is the third great natural source of heat? I will ask Mr. Hume."

"Mechanical action, or force trans.m.u.ted to heat."

"Will you please explain this?"

"Strictly speaking," said Mr. Hume, "this is not to be counted an original source of heat. But heat is used in the production of winds and waves, the flow of rivers, and all the ceaseless activities of the world, and this force reappears from time to time trans.m.u.ted again to heat. Whenever in the friction of air and of water, in the dashing of matter against matter and force against force, motion and force seem to be lost, heat is produced. The water of the sea after long storms is said to be sensibly warmed. We can appreciate the amount of heat generated in this manner only by considering in how many thousand ways force is meeting force and motion is destroyed. All this lost motion--lost as sensible motion--reappears as atomic motion, that is, as heat. Such heat has been applied to artificial uses. Heat generated by the friction of iron plates ground together has been used for heating buildings."

"And this trans.m.u.tation of living force and heat," added Mr. Wilton, "is but one of many ill.u.s.trations of G.o.d's economy in the management of heat.

Nothing is wasted. The voices of Nature all echo the words of Jesus: 'Gather up the fragments, that nothing be lost.'

"The fourth source of heat is chemical action. What is the chief form of this which is used for the production of heat? Samuel may tell us."

"Combustion, I think, sir."

"That is right; and the most common form of combustion is the combination of carbon with oxygen. This is commonly employed, not because it generates the most intense heat, but because carbon exists so abundantly, and is the most available and the cheapest. The most common form of carbon is wood and coal. This is that storehouse of heat which G.o.d has placed in man's keeping. Without this the larger part of the earth's surface would be uninhabitable. This renders culture and civilization possible. Without it the arts could have no existence. The key of this storehouse of heat G.o.d has given to man, so that he may enter in and use its treasures at his pleasure. In the finer arts where very great heat is required, hydrogen is used in place of carbon. Jets of oxygen and hydrogen gas thrown together const.i.tute what is called the oxy-hydrogen blowpipe, and generate the intensest heat which can be produced by man.