tion of Sibylline leaves that had been first stirred by the wind. Not only were things not always as they seemed, but outside of the very simplest phenomena, everything was utterly different from what it seemed. Almost everything was really just the reverse of what it seemed, and the universe was a vast paradox. The sky seemed to be a great vault of solid matter which he called for this reason a "firmanent." The heavenly bodies seemed to move across this vault at varying rates, and their reappearance led to the notion that they revolved around the great level cake of earth and water on which he dwelt. The invisible air and other gases were likened to mind or spirit. All natural causes were explained after the analogy of human effort in the intentional production of effects, and the earth and air were peopled with invisible and often malignant spirits as the only recognized agents. And thus were built up great systems of magic, superstition and mythology. The errors thus forced into man's mind came to receive the sanction of religion which rendered it vastly more difficult to dislodge them. This herculean task has been the mission of science, for the truth lies deeply buried under this mass of error at the surface and can only be brought to light by the most prolonged and patient research in the face of this time-honored prejudice. The progress of man and society has been strictly proportioned to the degree to which hidden realities have thus been substituted for false appearances.
As a somewhat anomalous but very important example of the erroneous ideas which the human race must needs acquire and reluctantly surrenders may next be considered the optimistic habit of thought. Optimism can scarcely be called a doctrine. It does not result, like most erroneous beliefs, from a false interpretation of the facts which nature presents to the untrained faculties. It is rather the original, unreflective state of the pre-social mind. It is the survival of the most useful of all instincts, that of self-preservation. It was well adapted to that state, because to the animal it mattered not whether it was true or false. It is still a useful attitude to the swarming millions of human beings who do not reflect. But for it the realization of their
