entific era of the world's history. Newton, or rather Newton as developed by Laplace and the French school of mathematicians, entirely changed the whole aspect of things. Laplace, with propriety, described his great work by the title of 'Celestial Mechanics': the purpose of the work, which it effected with singular skill, was the reduction of the whole system of the heavens to the condition of an ordinary mechanical problem—a problem, too, having the advantage that the bodies concerned are all moving in vacuo, and that therefore there are none of the difficulties of friction, resistance of the air, and the like, which interfere with the easy solution of terrestrial dynamical problems. To the mathematician the solar system is a set of small bodies, which for some purposes may be even regarded as particles, revolving in connection with one much larger and central body, under the action of mutual gravitation according to a certain simple law; while the earth, regarded by itself and with reference to the phenomena of its own revolution, is a rigid, slightly oblate spheroid, the motion of which in given circumstances constitutes one of the prettiest problems of rigid dynamics. It is difficult perhaps for any one, who has not gone through the study pesonally and practically, to conceive how completely to the mind of a mathematician the solar system resolves itself into a problem of bodies in motion in vacuo. But, as soon as the mind apprehends the solar system thus, it has found an instance of the uniformity of Nature upon a very large scale. The mathematician who is capable of solving the problem of the planetary motions, as Laplace and Lagrange solved it, or who knows anything of the motion of a rigid body revolving as the earth revolves, finds himself simply incapable of conceiving of anything but motion, according to fixed law, being found in the solar system; the uniformity of Nature in this department presses itself upon him with a power which he can not resist.
A mathematician, for example, would find himself entirely precluded from sympathizing, in the most distant manner, with the view expressed by Mr. Ruskin at the meeting of the Metaphysical Society. The standing still of the sun, of which Mr. Ruskin speaks so pleasantly, means the stopping of the revolution of the earth, for the motion of the sun is only the earth's revolution; consequently, what is called the standing still of the sun involves tremendous dynamical consequences, an utter disruption of everything upon the earth's surface, a return of chaos, or I know not what. I am not criticising the expression as to the sun standing still, used in the book of Joshua without any attempt at scientific language. What the actual fact was to which the language used refers, and what was the actual phenomenon, I can not undertake to say; but if we adopt the phrase into the language of the nineteenth century, and in that language speak of the news of the sun standing still as a thing which need not surprise us, but which we have rather expected than otherwise, then I
