To the superﬁcial observer scientiﬁc truth is unassail-able, the logic of science is infallible; and if scientiﬁc men sometimes make mistakes, it is because they have not un-derstood the rules of the game. Mathematical truths are derived from a few self-evident propositions, by a chain of ﬂawless reasonings; they are imposed not only on us, but on Nature itself. By them the Creator is fettered, as it were, and His choice is limited to a relatively small number of solutions. A few experiments, therefore, will be suﬃcient to enable us to determine what choice He has made. From each experiment a number of consequences will follow by a series of mathematical deductions, and in this way each of them will reveal to us a corner of the universe. This, to the minds of most people, and to stu-dents who are getting their ﬁrst ideas of physics, is the origin of certainty in science. This is what they take to be the rôle of experiment and mathematics. And thus, too, it was understood a hundred years ago by many men of science who dreamed of constructing the world with the aid of the smallest possible amount of material borrowed from experiment.