energy and structure, are closely connected: to determine the exact relations existing between these, under stated conditions, is still the fundamental problem of chemical science.
We can define energy: the phlogisteans could not define phlogiston. But in the ethereal philosophy of the future will it not be said of the present workers in science that they could not define ether, but even spoke of it at times as "not gross nor ponderable matter"? The theory of phlogiston was continued and developed in the theory of caloric: the theory of caloric is vastly extended, simplified, and rendered definite in the theory of energy, and the theory of energy seems destined to be largely extended by the ethereal theory now in its infancy.
Mankind has until lately been content with space of three dimensions, but the bolder and more dashing spirits among the mathematicians have dared to look forward to a better world than this where they may revel in space of four dimensions. What a strange world must that be! what a fearful place for a mathematical examination, when we remember that the inhabitants thereof—if there be inhabitants—may turn spherical hollow balls inside out without tearing or breaking them!
While we look forward to the future of science with hope, I think we ought not to look back on the former workers without respect.
But I must pass on to consider the second of the great theories which have paved the way for the doctrines of modern chemistry. The germ of the modern ideas of substitution, valency, atom-linking, etc., is, I believe, to be found in the pure dualism of Berzelius; and, moreover, the influence of the dualistic ideas of that great chemist seems to me easily traceable in the essentially unitary system of modern chemistry. The chemistry of Lavoisier centered around the wonderful substance whose properties he so carefully studied. The teaching of the great founder of modern chemistry was saturated with ideas suggested by the study of oxygen. The compounds of oxygen were divided by Lavoisier into two groups, bases and acids: when these reacted chemically, a salt—that is, a body made up of base and acid—was produced. Berzelius developed these ideas until he had constructed a complete and beautiful theory, viewed in the light of which all compounds were of analogous structure. Every chemical substance was made up, according to the Swedish chemist, of two parts; these parts might themselves be composed of simpler parts, or they might be truly elementary. The two parts of a compound were respectively endowed with positive and negative electricity. When two bodies combined, the positive electricity in one neutralized the negative electricity in the other; hence the phenomena of light and heat noticed in chemical combination. An element might contain an absolutely greater quantity of positive electricity than another and nevertheless belong to the electro-negative series of elements: thus sulphur and oxygen readily combine to form a substance which, when dissolved in water, yields an
