voyager in strange seas of thought alone might resort with confident hope of renewing his youth. Turning his back on Karl Pearson and England, he plunged into Germany, and had scarcely crossed the Rhine when he fell into libraries of new works bearing the names of Ostwald, Ernst Mach, Ernst Hæckel, and others less familiar, among whom Hæckel was easiest to approach, not only because of being the oldest and clearest and steadiest spokesman of nineteenth-century mechanical convictions, but also because in 1902 he had published a vehement renewal of his faith. The volume contained only one paragraph that concerned a historian; it was that in which Hæckel sank his voice almost to a religious whisper in avowing with evident effort, that the “proper essence of substance appeared to him more and more marvelous and enigmatic as he penetrated further into the knowledge of its attributes, — matter and energy, — and as he learned to know their innumerable phenomena and their evolution.” Since Hæckel seemed to have begun the voyage into multiplicity that Pearson had forbidden to Englishmen, he should have been a safe pilot to the point, at least, of a “proper essence of substance” in its attributes of matter and energy; but Ernst Mach seemed to go yet one step further, for he rejected matter altogether, and admitted but two processes in nature, — change of place and interconversion of forms. Matter was Motion, — Motion was Matter, — the thing moved.
A student of history had no need to understand the scientific ideas of very great men; he sought only the relation with the ideas of their grandfathers, and their common direction towards the ideas of their grandsons. He had long ago reached, with Hegel, the limits of contradiction; and Ernst Mach scarcely added a shade of variety to the identity of opposites; but both of them seemed to be in agreement with Karl Pearson on the facts of the supersensual universe which could be known only as unknowable.
With a deep sigh of relief, the traveller turned back to France. There he felt safe. No Frenchman except Rabelais and Montaigne had ever taught anarchy other than as path to order. Chaos would be unity in Paris even if child of the guillotine. To make this assurance mathematically sure, the highest scientific authority in France was a great mathematician, M. Poincaré of the Institut, who published in 1902 a
