laws of thought. No psychological theory has greater probability than that which bases the units of knowledge in experience. Since the time of Locke and Hume, the drift of speculation has been steadily in the direction of a more or less modified empiricism. The more far-sighted of the intuitionists cast aside everything they thought could embarrass their theory, and were content to allow that the matter of thought was based upon experience, while reserving as the province of intuition the mental forms by which knowledge was possible. The theory of evolution explains this intuitional residue by extending the experience of the individual to the experience of the race, and showing that what may be intuitive (in every sense, except the supernatural, in which that word was formerly used) to the individual is so in consequence of inherited tendencies corresponding to the aggregate experience of his ancestors.
But we do not need to urge mental theories, however probable, to show that our knowledge of the universe is dependent upon our surroundings. A little difference in the physical condition of the earth would have sufficed to have utterly changed our conception of nature. Make the not very inconceivable supposition that our earth bore the same relation to the sun that the moon does to the earth—rotating once on its own axis to each revolution about the sun, and remaining nearly perpendicular to the ecliptic, thus always presenting the same side to the sun's rays—how would it have affected our knowledge of nature? To what modest proportions would not only science have shrunk, but also our mental or intuitive conceptions of nature!
Astronomy has been well called the mother of the sciences. The apparent motions of the sun, moon, and stars through the heavens, and the motions of the planets among the stars, contributed to produce a wonder in the minds of the beholders that might well cause astronomy to be the first studied of the sciences. In our hypothetical world, the sun would appear stationary in the heavens, more or less removed from the zenith according to the position of the observer. On the center of the earth's surface would be a torrid zone upon which the vertical rays of the sun would pour down with unremitting severity, with no alternation of day and night to temper its influence. Outside of this would be a temperate zone well adapted, it might be, to the existence of human beings, but having no change of seasons, only one monotonous summer day, varying in temperature according to location. The temperate zone would gradually give place to a frigid zone, and, as the day darkened into an eternal night, this would be succeeded by an impenetrable region in which the degree of cold would vastly exceed anything we have on earth at present. Thus man, confined to somewhat less than half the globe, would see nothing of the moon or stars, and the earth, with the sun shining on it, would be the only bodies visible. There would be no natural divisions of time into days, weeks, months, or years. Mathematicians might calculate the hemispherical
