We know that those atoms obey certain conditions which appear to be dependent upon the influences of motion, gravitation, heat, light, electricity, and chemical force. These powers are only known to us by their effects; we only detect their action by their operations upon matter; and although we regard the several phenomena which we have discovered, as the manifestations of different principles, it is possible they may be but modifications of some one universal power, of which these are but a few of its modes of action. In examining, therefore, the truths which science has revealed to us, it is advantageous, for the purpose of fixing the mind to the subject, that we assume certain conditions as true. These may be stated in a few sentences, and then, without wasting a thought upon those metaphysical subtleties which have from time to time perplexed science, and served to impede the progress of truth, we shall proceed to examine our knowledge of the phenomena which constantly occur around us. Every form, whether inorganic or organic, which we can discover within the limits of human search, is composed of atoms, which are capable of assuming, under the influence of certain physical forces, conditions essential to the physical state of that body of which they constitute a part.[1] The known forces, active in producing these conditions, are modes of motion; gravitation and aggregation, heat, light; and associated with these, actinism or chemical radiation; electricity, under all its conditions, whether static or dynamic; and chemical affinity, regarded as the result of a separate elementary principle. These forces must be considered as powers capable of acting in perfect independence of each other. They are possibly modifications of one principle; but this view being an hypothesis, which, as yet, is only supported by loose analogies, cannot, without danger, be received in any explanation which attempts to deal only with the truths of science. We cannot examine the varied phenomena of nature, without feeling that there must be other and most active principles of a higher order than any detected by science, to which belong the important operations of vitality, whether manifested in the plant or the animal. In treating of these, although speculation cannot be entirely avoided, it will be employed only so far as it gives any assistance in linking phenomena together. We have to deal with the active agencies which give form and feature to nature--which regulate the harmony and beauty and vigour of life--and upon which depend those grand changes in the conditions of matter, which must convince us that death is but the commencement of a new state of being. FOOTNOTES: [1] Sir Isaac Newton supposed matter to consist of hard, impenetrable, perfectly inelastic atoms.