Some of the most interesting discoveries about radioactivity are very recent. Radium prepared from uranium in 1915 was found in 1919 to have increased proportionately to the square of the time interval. The amount of radium in some preparations was found to have increased ten times in four years. The old idea of the constant fluxation of matter was thus shown to have been based upon a scientific truth. CHAPTER XVII SCIENCE IN THE TWENTIETH CENTURY It is obvious that we are now in a great period of transition. Scientific discoveries came so quickly at the end of the last century that a recasting and readjusting of scientific conceptions had to be undertaken. This process was in progress when the World War began. The world-wide disturbance led to temporary scientific infertility except in such directions as served the purposes of war. But therein science became allied more closely than ever before with certain branches of industry, and the cooperation thus established has been recognized in all civilized countries as of the utmost value to the future progress of mankind. The philosophic thought of each era generally develops in harmony with social and intellectual conditions. The philosophical doctrines of the leading writers may, therefore, be taken as representative of the spirit of their age. When Darwin in the middle of the last century published his doctrines of evolution, of the struggle for existence and the influences of living conditions upon survival of species, philosophy turned away from the utilitarianism and tolerance of Hamilton, Hume, and Mill and the positivism of the French to the synthetic evolutionism of Herbert Spencer. One of the basic teachings of Spencer was the relativity of knowledge. The process of thinking involves relation, difference, and likeness. This is merely relationing. Therefore no thought can ever express more than relations. The primary act of thought through which we discover likeness and difference underlies all our knowledge. A reaction against this new empiricism began in 1898, when William James published his "Philosophical Conceptions and Practical Results." This work popularized the philosophy of pragmatism which denies the absoluteness or ultimateness of the traditional antithesis between theory and practice and relies for its justification upon the fact that everything which we think about, and do, must first be willed. Reality consists in pure experience quite independent of thought. Bergson developed this philosophy of practicalism further and taught that knowledge of reality comes through intuition and that life is merely intuitive knowledge. Intuition, is deeper than scientific reason because it feels, and links us with, the eternal processes of nature.