another lord’s day comes, and no change has taken place with the class 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[pg 293] 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 gods and brought it to men in his reed staff, but fire is certainly worthy of being counted one of god’s great gifts. but whence comes the heat of combustion? is it a new and original [pg 294]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 transmutation 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[pg 295] 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[pg 296] 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 shell 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[pg 297] 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 mass 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.”

[pg 298]“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 mass 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[pg 299] 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[pg 300] fires, but a sublime illustration 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 god 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 mass 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[pg 301] 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 mass would assume 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[pg 302] 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 mass 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 mass, 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 class 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 god’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 god is shown. my thoughts of the[pg 303] 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 god 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 [pg 304]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 god.’ this light has shone upon me for many years.”