the food for our iron horse developed from the great store-houses of nature in a rapidly increasing measure, just as the creature is developed into a perfect life, but we also discover the work it is being called upon to perform. Its family is growing by thousands a year, while its habitat, the railroads, are multiplying in endless ratio. The iron steamers of the sea, too, and of the great inland routes of commerce, are, and are to be, insatiable in their demands for this great generator of strength for iron arms and sinews. Europeans, if not Americans, are demonstrating that iron steamships can carry much cheaper than sailing vessels, the time taken for trips considered, because vessels propelled by steam are gradually superseding sailing vessels. It is probable that coal will ere long be included among those articles that are reckoned as contraband of war. Now that steam is destined to play an important part in naval warfare, the coal by which steam is produced is certainly entitled to a prominent place among munitions de guerre.

Nearly all the coal consumed in London was taken there by coastwise vessels from Newcastle and elsewhere forty years ago (1832), while within that period the transportation into London, by railways alone, has grown to be equal to that taken by vessels, and the amount carried by the latter is fifty per cent. in excess of what it was then; meantime, its average price has not increased there. In this no mention is made of the tonnage required on railways for distributing coal to the manufacturing and other districts of Britain. Herein may be seen outlines of a future traffic, huge in proportions, yet to be acquired by the railroads of the Western States of the Union, not to name others.

The importation into the United States of what has been for many years known on the Atlantic coast as "Liverpool coal " has always been considerable; so late as 1865 the amount was 134,ooo, tons; an ugly fact in view of our greater supplies. The productive coal measures of the United States exceed those of all the rest of the world, as at present known, and the greatest fields of coal in the Union are in the districts of the Mississippi Valley, already pointed out.

Coal, for most purposes, is much better than wood; but, in fact, the two, although in appearance so different, are, in their ultimate composition, very nearly allied. They both have for their basis. or chief ingredient the substance called by the chemists carbon, and their chief other ingredient, the substance called hydrogen, which, when separated, exists in the form of gas. The hydrogen is easily driven away or volatilized from either coal or wood, by heating in a close place; and when it is caught and preserved, it forms the gas now used to light the streets and buildings of our cities and larger towns. What remains of coal after being so treated is the substance called coke, referred to in this article as used in running locomotives on the English railways; and what

remains of wood, similarly treated, is the substance called charcoal; both being nearly pure carbon, but differing as to the states of compactness This kindred nature of coal and wood does not surprise us when the fact is known that much of our coal is really transformed wood; many coal-mines being evidently the remains of antediluvian forests, swept together in the course of terrestrial changes, and afterward solidified to the state now seen. The species of the plants or trees which formed them are often quite apparent. The extensive beds of peat moss or turf, now existing on the surface of the earth consist chiefly of vegetable remains in an early stage of change, which finally terminates in the formation of coal.

The phenomenon of common fire or combustion is merely the fuel being chemically dissolved in the air of the atmosphere. If the fuel has nothing volatile in it, as is true of pure carbon, and nearly true of coke and charcoal, it burns with the appearance of red-hot stones; but if there be an ingredient, as hydrogen, which on being heated, readily assumes the form of air, that ingredient dilates before burning, and in the act produces the more bulky incandescence called flame.

The two great purposes which combustion serves to man are to give light and heat. By the former he may be said to lengthen considerably the duration of his natural existence; for he converts a portion of the almost useless night into what, for many ends, serves him as well as day; and by the latter, besides converting winter into any climate-within doors-which he desires, he is enabled to effect most important mutations in many of the substances which nature offers for his use; and since the invention of the steam-engine, he makes heat perform a great and constantly increasing proportion of the work of society. From these considerations may be perceived the importance of having fire at command; and as the cheapest means of commanding fire, of having abundance of coal. By it our dwellings are lighted and heated, and thus made more comfortable; with it the steam-engine may be fed, labor lifted from our shoulders and taken from our hands, and we may be enabled comfortably to go with railroad and steamer speed to the ends of the earth.

From an admirable article by Robert Hunt, F. R. S., we make the following extract on

66 'COAL AS A RESERVOIR OF POWER."

"The sun, according to the philosophy of the day, is the great store-house of force. All the grand natural phenomena are directly dependent upon the influence of energies which are poured forth without intermission from the central star of our system. Under the influences of light, heat, actinism, and electricity, plants and animals are produced, live and grow, in all their

infinite variety. Those physical powers, or, as they were formerly called, those imponderable elements, have their origin in one or other of those mysterious zones which envelope the orb of day, and become evident to us only when mighty cyclones break them up into dark spots. Is it possible to account for the enormous amount of energy which is constantly being developed in the sun? This question may be answered by saying that chemical changes. of the most intense activity are discovered to be forever progressing, and that to these changes we owe the development of all the physical powers with which we are acquainted. In our laboratory we establish, by mechanical disturbance, some chemical phenomenon, which becomes evident to our senses by the heat and light which are developed, and we find associated with them the principal which can set up chemical change and promote electrical manifestations, We have produced combustion, say, of a metal, or of a metallic compound, and we have a flame of a color which belongs especially to the substance which is being. consumed. We examine a ray of light produced by that flame by passing it through a prism, and this analysis informs us that colored bands, having a fixed angle of refraction, are constant for that especial metal. Beyond this, research acquaints us with the fact that, if the ray of light is made to pass through the vapor of the substance which gives color to the flame, the lines of the spectrum which were chormatic become dark and colorless.

SUNSHINE AND COAL BEDS.

"We trap a ray of sunlight, and we refract it by means of a spectroscope, when we detect the same lines as those which we have discovered in our artificial flame. We pursue this very interesting discovery, and we find that several metals which give color to flame, and produce certain lines, when subjected to spectrum analysis, are to be detected in the rays of the sun. Therefore our inference is, that some substances, similar to the terrestrial bodies, with which we are familiar, are actually undergoing a change in the sun, analogous to those changes which we call combustion; and, more than this, we argue that the high probability is, that all solar energies are developed under those conditions of chemical change-that, in fact, the sun is burning, and while solar matter is changing its form, Force is rendered active, and as ray-power passes off into space as light, heat, etc., to do its work upon distant worlds, and these forms of Force are expended in doing the work of development on those worlds. This idea theory-call it what you may-involves of necessity the waste of energy in the sun, and we must concede the possibility of the blazing sun's gigantic mass becoming eventually a globe of dead ashes, unless we can comprehend some method by which energy can be again restored to the inert matter. Certain it

is that the sun has been shining thousands of years, and its influence on this earth we know to have been the production of organized masses, absorbing the radiant energies, in volumes capable of measurement. On this earth, for every equivalent of heat developed, a fixed equivalent of matter has changed its form; and so likewise is it with regard to the other forces. On the sun, in like manner, every cubic mile of sunshine represents the change of form of an equivalent of solar matter, and that equivalent of matter is no longer capable of supplying Force, unless by some conditions, beyond our grasp at present, it takes up again that which it has lost. That something of this kind must take place is certain. The sun is not burning out. After the lapse of thousands of years we have the most incontrovertible evidence that the light of to-day is no less brilliant now than it was when man walked amid the groves of Eden. We may venture farther back into the arcana of time, and say that the sun of the past summer (1872) has shone with splendor equal to the radiant power which, myriads of ages ere man appeared on this planet, stimulated the growth of those luxuriant forests which perished to form those vast beds from which we derive our coal. Not a ray the less is poured out in any hour of sunshine; not a grain-weight of matter is lost from the mass of the sun. If either the sunshine were weakened, or the weight of the vast globe diminished, the planets would vary in their physical conditions, and their orbits would be changed. There is no evidence that either one or the other has resulted. Let us see if we can guess at any process by which this stability of the solar system is maintained.

"It was first shown by Faraday, in a series of experimental investigations which may be regarded as the most beautiful example of inductive science with which the world has been favored since Bacon promulgated his new philosophy, that the quantity of electricity contained in a body was exactly the quantity which was necessary to decompose that body. For example, in a voltaic battery of zinc and copper plates-a certain fixed quantity of electricity is eliminated by the oxidation of a portion of the zinc. If, to produce this effect, the oxygen of a given measure of water -say a drop-is necessary, the electricity developed will be exactly that which is required to separate the gaseous elements of a drop of water from each other. As equivalent of electricity is developed by the oxidation of an equivalent of zinc, and that electricity is required for the decomposition of an equivalent of water, or the same quantity of electricity would be equal to the power of effecting the re-combination of oxygen and hydrogen, into an equivalent of water. The law which has been so perfectly established for electricity is found to be true of the other physical forces. By the combustion-which is a condition of oxidationof an equivalent of carbon, or of any body susceptible of this

change of state, exact volumes of light and heat are liberated. It is theoretically certain that these equivalents of light and heat are exactly the quantities necessary for the formation of the substance from which those energies have been derived. That which takes place in terrestrial phenomena is, it is highly probable, constantly taking place in solar phenomena. Chemical changes, or disturbances analogous to them, of vast energy, are constantly progressing in the sun, and thus is maintained that unceasing outpour of sunshine which gladdens the earth, and illumines all the planets of our system. Every solar ray is a bundle of powerful forces; light, the luminous life-maintaining energy, giving color to all things; heat, the calorific power which determines the conditions of all terrestrial matter; actinism, peculiarly the force which produces all photographic phenomena; and electricity regulating the magnetic condition of this globe. Combined in action, these solar radiations carry out the conditions necessary to animal and vegetable organization, in all their varieties, and create out of a chaotic mass forms of beauty rejoicing in life.

"To confine our attention to the one subject before us. Every person knows that, to grow a tree or shrub healthfully, it must have plenty of sunshine. In the dark we may force a plant to grow, but it forms no woody matter, it acquires no color; even in shade it grows slowly and weak. In sunshine it glows with color, and its frame is strengthened by the deposition of woody matter eliminated from the carbonic acid of the air in which it grows. A momentary digression will make one point here more clear. Men and animals live by consuming the products of the vegetable world. The process of supporting life by food is essentially one of combustion. The food is burnt in the system, developing that heat which is necessary for life, and the living animal rejects, with every expiration, the combinations, principally carbonic acid, which result from this combustion. This carbonic acid is inhaled by the plant; and, by its vital power, excited by sunshine, it is decomposed; the carbonic forms the ligneous structure of the plant, and the oxygen is liberated to renew the healthful condition of the atmosphere. Here we see a sequence of changes analogous to those which have been shown to be a law of electricity."

HOW WOOD AND COAL ARE DEVELOPED.

Every equivalent of matter changing form in the sun sends forth a measured volume of sunshine, charged with the organizing powers as potential energies. These meet with the terrestral matter which has the function of living, and they expend themselves in the labor of producing a quantity of wood, which represents the equivalent of matter which has changed form in the sun. The