the flowing of waters, the transformations of chemistry, the operations of vitality, and the revolutions of the heavenly bodies.

But as the ancients never explained the laws by which elementary caloric operates in the generation of force and motion, nor the manner in which it is related to electricity and light; their speculations have exerted little influence on the physical theories of modern philosophers, who have, strangely enough, disregarded nearly all that was most valuable in the science of antiquity. At the present time, it remains undecided, whether caloric is an exceedingly subtile and active essence, as maintained by the early Hindoos, Egyptians, Phoenicians, Chaldeans, Persians, and Arabians, as well as the more enlightened Greeks and Romans; or whether it consists in mere motion and vibration among the particles of ponderable matter, as supposed by Bacon, Boyle, Hooke, Rumford, Davy, Young, and others.

One of the most important modern discoveries was that of latent or combined heat, by Dr. Black. When he proved by accurate experiments, that definite measures of caloric are required to convert solids into liquids, and that

the same subtile fluid is obtained from the atmosphere by respiration, he laid the foundation of its true theory. But as he did not extend his researches to its agency in the mechanical, chemical, and vital phenomena of nature, his labours have not been followed by results corresponding with the magnitude of his discovery, if we except the improvement of the steam engine by Watt.

Nor has any one, either among the ancients or moderns, ever attempted to give a regular and systematic history of the mode in which caloric operates in all the molecular and aggregate forces of matter. Mr. Whewell observes, in his late History of the Inductive Sciences, that "we have no hypothesis regarding thermotics, which, being assumed in order to explain one class of phenomena, has been found to account exactly for another." Yet he adds, "it is one of the cardinal points on which the doors of physical knowledge must turn, which have hitherto remained closed."

Within the last hundred years, electricity has been regarded by many persons as a key by which to unlock all the secret cabinets of nature. We have had electrical theories of chemistry, of life, and of the universe. Yet

no one has explained what electricity iswhether a separate and distinct agent-a modification of some other exceedingly refined and more comprehensive principle—or a mere effect, condition, or property of ponderable matter. The celebrated Faraday at one time adopted the simple and rational theory of Franklin, that it is a material fluid, definite measures of which belong to each element of ponderable matter. And yet he speaks of it very often as if he considered it to be a compound fluid. But when treating of its chemical agency, he represents it as "a modification of the exertion of chemical forces."

Again; when by following up the discoveries of Erstedt, Davy, Arago, and Schweigger, who found that electricity is capable of producing all the phenomena of magnetic action on a small scale, he succeeded in obtaining an electric spark from a permanent magnet; he arrived at the conclusion that electricity and magnetism are identical; except that in the latter " the axis of power" is greater than in the former. Yet, as if not satisfied with any of the foregoing hypotheses, he suggests, at another time, that electricity may be resolved into undulations of an æther;

and, at another time, that all the more important electrical phenomena may be resolved into polarization of the particles of ponderable matter, or what has been called atomic polarity. But he does not explain what he means by the axis of power, and electric polarity; nor how chemical affinity and magnetism, which are merely effects or modes of action, can be identical with their cause; nor does he inform us what causes the æther to vibrate. Such have been the difficulties of this important department of physical science, that its most distinguished votaries have hitherto failed to present us with a consistent theory of electrical phenomena. But I hope to make it appear that most of these perplexities have arisen more from defective methods of inquiry, than from any inherent obscurity of the subject.

Among the physical speculations of Oken, light, heat, and weight, are represented as a trinity of powers, to which all the phenomena of nature may be referred: while it was maintained by Coleridge, that electricity, galvanism, and magnetism, are the three fundamental principles of action in nature, and identical with the three primary dimensions of space—length, breadth, and depth. Yet, he observes, that

"the sole factors in all electrical phenomena consist in attractive and repulsive forces, independent of any material substrate." Such is the reverence of mankind for mysteries, that the most obscure and visionary fancies are often regarded as profound. It was long ago remarked by Longinus, that darkness is a source of the sublime: and it must be admitted that objects are magnified by looming through a fog.

In all ages of the civilized world, light has been recognised as a powerful agent in the work of the universe. As the great painter of nature, it gives to the dome of heaven its azure hue, to the rainbow, its gorgeous red, brilliant yellow, refreshing green, and lovely blue, shading into the softer violet. It is solar light which touches the morning and evening clouds with its celestial pencil, when they glow with vivid tints of ruby, sapphire, and gold. It adorns the flowery fields with an endless variety of beauteous colours; while it is perpetually modifying the taste, odour, and other sensible properties of whatever it touches.

But it is still an unresolved problem, whether light be a material substance, as maintained by Pythagoras, Democritus, Leucippus, Empedocles, Plato, Epicurus, Newton, and Brew