his theory of values, while phrases like Natural Selection and the doctrine of evolution recall Darwin and Spencer. Words and phrases alike point to a struggle for condensation of thought in terms so clear and simple that no one can mistake their meaning.
Inasmuch as science has become international and we no longer speak of it as French, English or German, but simply as science, something in which all seekers after truth have a common ownership, a few of those explanations of the universe may now be considered which "exact thought" has given. We may look first of all at the abstract views, four in number, which are ancient in their origin, mathematical in their form and are still ardently defended. These are what have been termed the astronomical view of the world, the atomic view, the kinetic view and the physical view. The latter is the explanation given by those who believe in energy as the underlying and directing cause of movements or changes in the universe.
The astronomical theory rests on the doctrine of gravitation and explains the phenomena of the world in which we live as well as the relation and movements of the heavenly bodies to each other by the assumption of its universal existence. Upon the principle that bodies attract each other directly as their mass, inversely as the square of their distance, Newton enunciated his law of falling bodies. Upon this same principle the tides were explained as well as the revolution of the earth on its own axis and round the sun, the rotation of the heavenly bodies around their axes and around the sun, their motion through space and the velocity of this motion. If gravitation is universally operative on the earth, why should it not be operative everywhere? Through aid of the calculus Newton was able to apply the law of gravitation with the utmost accuracy and by its application lay bare the secrets of the heavenly bodies.
Newton's principles were received more favorably in France than in England. Under the influence of Laplace and the Paris Academy of Sciences, in spite of the protest of a sceptic here and there these principles were, after thorough and somewhat bitter discussion, accepted as true in France, and in no long time in all Europe. On Newton's theory of gravity, the corpuscular explanation of light made its way in scientific circles. Light was believed to be a substance and its laws of reflection and refraction were explained by the law of falling bodies.
The discovery of magnetism in 1791, of the voltaic pile in 1800, and researches into the phenomena of electricity, together with a growing conviction that space is empty and that matter is composed of atoms and requires a void, weakened confidence in the astronomical theory as a full and satisfactory explanation of all the phenomena of the universe. No one denied the facts which Newton had brought forward. No one ventured to assert that gravitation does not act everywhere, or that its