ster; or whether it consist in the mere vibrations of some unknown æther, as supposed by Huyghens, Hooke, Euler, Young, Sir John Herschel, Arago, and others. Nor is it yet finally settled whether white light is composed of seven primitive rays, as supposed by Newton, or of only three fundamental colours, as maintained, with many cogent reasons deduced from experiment, by Sir David Brewster. On the same subject, the advocates of the undulatory or wave theory are equally at variance among themselves for while Huyghens maintained that solar light is composed of only two elementary colours, yellow and blue, Hooke reduced all its modifications to red and violet; whereas Young reduced the whole to red, green, and violet.

What is still more remarkable, neither of the two great rival parties has ever yet attempted to ascertain the relations of light to caloric and electricity; nor in what way they perform so many wonderful effects in the moving drama of the universe. But if they be connected in action, they must be united in theory. And it will be a leading object of the following work to prove, by a careful generalization of facts, that caloric and electricity are mutually convertible into each other; consequently, that

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they are modifications of one and the same essence, which is the active principle in light, and in all the phenomena of nature.

Since the time of Sir Isaac Newton, it has been generally supposed that all the molecular changes of matter may be referred to attractive and repulsive forces. Yet the cause of attraction and repulsion has not been identified with any known principle capable of demonstration. The orbits of planets, and the times of their revolutions have been measured with mathematical precision; but the cause of their eternal motion has never been clearly distinguished from projectile and gravitating forces. The relative magnitudes of the particles or atoms of ponderable matter have been, to a certain extent, ascertained by the refined analyses of modern chemistry: yet the cause of chemical affinity is still confounded with inherent properties, occult qualities, and undefined powers. The composition of plants and animals has been discovered, and their intimate structure explored: yet the organizing principle remains a profound mystery. What was said by Descartes two hundred years ago, is equally true at the present day. In Philosophia nihil adhuc reperiri, de quo non in utramque partem disputatur."

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It has been a complaint of long standing in the world, that nature has spread a veil over the first principles of things, which man can never hope to remove. But there is reason to believe that all the great truths of science which are of the highest importance for us to know, are no less remarkable for simplicity, than for the wide extent of their application; and that when fully unfolded, they will be selfevident propositions. It is true enough, that the most familiar phenomena of nature, when viewed separately, or through the mystical interpretation of visionary theorists, are as

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inscrutable as the scattered leaves of the Sibyl:" but when traced to their origin, the hidden meaning of every thing is gradually disclosed, and order springs from chaos. It was profoundly observed by Sir Edward Bulwer, that "the key to all mystery is the desire to know,”—and that "there is only a single step from a truism to a great discovery.”

If we are destined ever to arrive at a perfect theory of nature, it must be founded on a true history of the grand original, and a complete knowledge of the prime mover. Nor is it possible that men should avail themselves fully of the powers which are in nature, without knowing the cause of these powers.

It

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was from the elastic force of the latent caloric that belongs to nitre, sulphur, and charcoal, that man, unconsciously, obtained the power gunpowder; the invention of which has essentially modified the condition of the human race: for it thenceforward secured the uninterrupted progress of civilization, which can never again be arrested by the incursions of barbarous hordes, nor the light of knowledge be extinguished in embryo, as during the early periods of history. It was by discovering that a piece of metal called the loadstone, when horizontally balanced on a pivot, is constantly directed to certain points in the polar regions, that commerce and civilization have been extended

to the remotest parts of the earth. But men have yet to learn that the same principle which directs the compass-needle to the poles, guides the planets in their orbits, and fills them with life.

It was by seizing the grand lever of nature as a moving agent, that man was enabled to create the steam-engine, which has brought about a more important revolution in the condition of nations, than all the united discoveries of antiquity for thousands of years. Nor can there be a reasonable doubt that a complete

knowledge of the same agent, as it operates in all the phenomena of nature, would augment the resources of happiness a thousand fold-dispel the clouds of error which have so long hovered over the sciences, and enlarge the empire of man over the material world, in an endless variety of ways. It is animating to think how soon this grand result might be brought about, if all the talents now wasted on fruitless speculations were rightly employed in the study of nature.

It may be right to inform the Reader that a brief outline of the leading views contained in the following chapters was first promulgated by the Author in an Essay entitled "A New Theory of Terrestrial Magnetism," published at New York in 1833; and somewhat extended in a series of papers in the Knickerbocker Magazine of 1834-5. The Author also feels it due to himself, and to those friends who have been long expecting this Work, to state, that the first three books were originally intended to be published separately, and were actually printed in 1837, the preliminary chapter excepted. But as more enlarged views of the subject opened to him, he clearly perceived that a development of the physiological and