inflexible course, often inspires in us a confidence nothing warrants, and prevents our looking about us.
From another point of view, however, the two conceptions are very unlike, and if all must be said, they are very unlike because of a common fault.
The English wish to make the world out of what we see. I mean what we see with the unaided eye, not the microscope, nor that still more subtile microscope, the human head guided by scientific induction.
The Latin wants to make it out of formulas, but these formulas are still the quintessenced expression of what we see. In a word, both would make the unknown out of the known, and their excuse is that there is no way of doing otherwise.
And yet is this legitimate, if the unknown be the simple and the known the complex?
Shall we not get of the simple a false idea, if we think it like the complex, or worse yet if we strive to make it out of elements which are themselves compounds?
Is not each great advance accomplished precisely the day some one has discovered under the complex aggregate shown by our senses something far more simple, not even resembling it—as when Newton replaced Kepler's three laws by the single law of gravitation, which was something simpler, equivalent, yet unlike?
One is justified in asking if we are not on the eve of just such a revolution or one even more important. Matter seems on the point of losing its mass, its solidest attribute, and resolving itself into electrons. Mechanics must then give place to a broader conception which will explain it, but which it will not explain.
So it was in vain the attempt was made in England to construct the ether by material models, or in France to apply to it the laws of dynamic.
The ether it is, the unknown, which explains matter, the known; matter is incapable of explaining the ether.
Poincaré.
INTRODUCTION
BY PROFESSOR JOSIAH ROYCE Harvard University
The treatise of a master needs no commendation through the words of a mere learner. But, since my friend and former fellow student, the translator of this volume, has joined with another of my colleagues, Professor Cattell, in asking