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space? It is plain that there must be some medium capable of receiving and transmitting the motions of the vibrating atoms, as the air receives and transmits those of vibrating bodies in the case of sound.* That air is not the medium by which heat is communicated, is proved by the fact that it is transmitted through a vacuum more readily than through the air. Even in the absence of experimental proof, we would be likely to reach the same conclusion theoretically; for it is easy to see that the atomic vibrations are too delicate, too rapid, and within too narrow limits, to be transmitted from one atom of the gross matter of the atmosphere to another across the wide space that must exist between them. We are thus led to the supposition that there must be another kind of matter pervading space, filling up the pores between the atoms of the atmosphere, and so subtile and refined, and so infinitely elastic, as to be capable of communicating these delicate vibrations of the heated atoms. This fluid has been called ether by physicists, who hold that its existence may be inferred from a series of refined and careful experiments instituted for the purpose of establishing the undulatory theory of light. We must admit, however, that, although the existence of this ether is almost universally accepted as a fact by scientific men, there must arise in the mind of a scientific skeptic serious obstacles in the way of its unqualified adoption; and that, even after it is adopted, there remain difficulties in the transmission of atomic vibrations still unexplained. Yet, since it is necessary to adopt some hypothesis, and as this is the only one which accounts for most of the phenomena, we must perforce accept it, at least until a better one is proposed. Besides, after having adopted it to explain the transmission of light, it is easy enough to receive it as the theory of the communication of heat. Its adoption is rendered still less difficult when the intimate relation between light and heat is considered. These two always accompany each other in the rays of the sun, and in all cases
*Newton considered some such medium necessary in the case of gravity. He says: "That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it." See Newton's Third Letter to Bentley.
of ordinary combustion. If we examine the solar spectrum, we will find their relation curiously illustrated. In the violet ray, where the undulations are the fastest, their amplitude the shortest, and the refraction the greatest, no heat at all is found. But as we approach the red ray, where the undulations are the slowest, their amplitude greatest, and the refraction least, the heat increases, and becomes most intense beyond the red, where there is no light at all. These facts plainly suggest the idea that light and heat are produced by the same kind of vibrations of the atoms, but that those of heat are slower and of greater amplitude than those of light. Chemical action would also fall into the same category; for as we go toward the violet end of the spectrum its actinic power increases, and becomes the greatest beyond the violet, where the undulations seem to be too rapid to affect the sense of sight at all. Sound furnishes an analogy to this. The slow and heavy vibrations of a sounding body, as in the case of thunder, the roar of a cannon, or even the lower tones of an organ, produce a corresponding jarring sensation over the whole surface of our bodies, and are felt, while the more rapid vibrations affect only the ear, and are heard. But when the vibrations exceed thirty-six thousand five hundred per second, they fail even to affect the sense of hearing. So the ethereal vibrations are capable of producing different kinds of impressions. While they are slow and of great amplitude, they affect our sense of feeling only, and produce heat; as the rapidity increases, our sense of sight is affected, and light is produced. But when the rapidity increases beyond a certain point, impressions are no longer made upon the eye, but chemical action is the result. In the homogeneous rays of the sun these vibrations, having different velocities and amplitudes, accompany each other, and the three effects, light, heat, and chemical action, are produced simultaneously. But, in consequence of the different refrangibilities of these sets of vibrations, arising from their different velocities, we are able, by means of the prism, to separate them from each other in the spectrum, and examine each one by itself.
Dr. Draper's beautiful experiments throw light on this point. By subjecting different substances to the action of heat, he found that as the body began to be heated the heat was of the lowest refrangibility, but increasing in refrangibility and energy
of vibration as the intensity of the combustion increased. When the temperature reached one thousand degrees, the heat-vibrations became rapid enough to affect the eye, and light was produced. As the temperature rose, the colors of the spectrum appeared successively in the order of their refrangibility-red, orange, yellow, green, blue, indigo, and violet. When the temperature reached two thousand one hundred and thirty degrees all the colors were produced, making white light, which, besides light and heat, was capable of producing chemical action, like the homogeneous white light of the sun. As the body became cool, the colors again made their appearance in the reverse order, the red disappearing below one thousand degrees.
Thus far we have only discussed the relation between light, heat, and chemical action. To these must be added electricity and magnetism, for it has been experimentally proved that the close mutual relations that exist between the others extend to these also. They all belong to the same group, and must be considered but different manifestations of the same force. Whenever any one of these forces is exerted, it is always accompanied by a collateral manifestation of one or more of the others. Examples of their mutual convertibility into each other are abundant. Thus, chemical action in the battery develops electricity in the conducting wire; the current in turn generates magnetism in a bar of soft iron at right angles to its course; if it be passed through an imperfect conductor, light and heat will be produced; and if passed through a compound in solution, chemical decomposition is the result; or, if we begin with any one of the series, by furnishing the proper conditions all the others may be produced in succession. Not only has the mutual correlation of these forms of force been experimentally shown, but the quantitative relation of all of them, except light, has also been determined, thus furnishing additional proof of the fundamental doctrine of the "conservation of force." That light has a fixed and definite relation to the other forces is to be presumed, though experiment has not yet determined its exact value. This is yet an interesting and promising subject for further research.
There yet remains one outstanding physical force of whose nature and relations we are as yet entirely ignorant-gravita
tion. All attempts to bring it under the law of the correlation and conservation of forces have thus far failed. That it is to remain an exception to this fundamental principle, no physicist, in view of the progress of the last few years, would be willing to admit. But, on the contrary, it is confidently believed that future investigation will reveal its true character and assign it its proper place in the family of correlated forces. There is no reason to doubt that, when the nature of polarity, or the condition of matter which gives rise to attraction and repulsion, is fully comprehended-and this difficulty is not now regarded as insuperable-it will be possible to explain all the wonderful phenomena of Universal Gravitation on the theory of ethereal undulations, and thus establish the complete identity of all the forms of physical force.
We may now see how great a step the adoption of this dynamical theory of heat, with all its practical and speculative results, has been toward the sublime end to which all philosophical thought and scientific investigation now seem to be tending. To demonstrate the grand unity and harmony of the forces producing all the endless variety of the phenomena of nature, is the great work which modern science has now presented to it. And, when we consider the earnestness and energy with which it has addressed itself to its work, we may hopefully look for results still more astonishing and far-reaching in their consequences than any yet obtained. For what has already been accomplished, wonderful and even startling as it may seem compared with our past knowledge, is really but indicative of the tendency of the great current of scientific thought, and prophetic of higher and wider triumphs yet to
ART. IV.—PHILANTHROPY IN WAR TIME.
The Philanthropic Results of the War in America. from Official and other Authentic Sources by an American Citizen. New York: Sheldon & Co. 1864.
IF we look back to the records of history we shall find-it may seem strange to say-that philanthropy, in its broadest sense, has always found the widest sphere of activity in war time. In the times of the Crusades, Christian maidens established along all the route of the army of the Crusaders hospitals for the sick and wounded soldiers, and ministered to their healing with such skill as they possessed; while at home, high-born matrons and maids gave from their own stores the food and clothing needed by the families of the men-at-arms who had followed their lords to the contest against the Paynim host.
In the civil war in England, which resulted in the dethronement and execution of Charles the First, not only were the sweet charities of domestic life called forth for the succor of the wounded, but education received a new and higher impulse; and from that period dates the foundation of some of the best institutions of learning in the land.
Not less productive of deeds of charity, though among a greatly impoverished people, was our own war of the Revolution. The sacrifices of the women of that period for the sake of the army, and the abundant contributions, even in the midst of the most grinding poverty, of all classes, mitigated greatly, though they could not wholly prevent, the sufferings of the soldiery. It was amid this fearful strife, too, that the foundations. of some of our best colleges were laid; and though the times seemed unfavorable for the promotion of education, yet our fathers, strong in their faith of the glorious future, determined to secure for their children the opportunities of instruction.
It is not, then, so utterly without precedent as our impulsive reader has assumed, that philanthropy should find ample field for exercise in time of war; though never has it attained to such extraordinary proportions as in the struggle in which we are now engaged, as indeed in no contest of modern times has there been so much occasion for its ministration.