Cartes, it was believed that circular motion was the natural motion.

Nor is the general acceptation of a theory any proof that it is the most true and most perfect theory that will ever be presented. How long endured the Ptolemaic system of astronomy, how firm was the belief of men in its truth! Those who first questioned it, those who first doubted that the sun revolved around the earth, were not only deemed unsound in reason, but "diabolical and wicked,” and were visited by the vengeance of the offended good sense of man. Extensive, too, was the sway of the theory of Des Cartes, which preceded the theory of gravitation. The Cartesian hypothesis, representing the worlds as moved by vortices of revolving matter, and the fall of bodies as motion downward by the decrease of the range of the vortex, they sinking to the lowest part of the whirlpool, held for a while an even contest with the hypothesis of gravitation, the battle hanging long with doubtful issue. Because it was decided at last in favor of the Newtonian school, is it to be supposed that the speculations of that truly great man, Des Cartes, were all absurd, that he affirmed no truth, that Newton was right in all his affirmations, and that the power of progress expired with his life? How great were Galileo, Copernicus, Leibnitz, Kepler! Yet who takes for granted all that they asserted? To see truth fitfully, through the obscurity of error, is the most that can be hoped for by any man, or can be claimed as the result of the labors of any philosopher.

Among the minds distinguished as far surpassing in power the range of ordinary intellects, was that of Kepler. He seemed, on some points at least, to have an intuitive perception of truth, and his discoveries have led to extended

practical results. His determinations of the laws of planetary motion are, and must ever continue to be, the basis of knowledge in astronomy. Yet even he believed that the carth was an animal, and many of his other ideas create a smile, they appear so fanciful and absurd; but fanciful and absurd because time and further observation have refuted them.

It is no evidence of a want of reverence for the great, that we believe and assert that no individual is without error or has attained the whole truth; that no authority, however great, should determine and settle every principle in philosophy. "There were giants in those days;" but so long as the race of man exists there will be strength.

"Why," said a very great man, far back in the ages of time, "why is it that neither very small nor very large bodies go far when we throw them, but in order that this may happen the thing thrown must have a certain proportion to the agent which throws it? Is it that the thing which is thrown must react against the thing which pushes it; and that a body so large as not to yield at all, or so small as to yield entirely and not to react, produces no throw or push?" Should the human mind have rested upon philosophy like this? By no means. The theories of philosophy are not truth, but monuments set up to mark the progress of man in his search for truth, guides in the path which leads to the truth. We should read with reverence for the great minds of olden times, while rejoicing in the advance which present opinions indicate; we should read present opinions in the belief that they also will servo future generations to mark a continued and accelerated progress; we should read with respect for those who have

faithfully discharged their trusts, and with confidence that those who are yet to do work upon the earth, will do it even more successfully, for having the vantage ground of former attainments, the highest reach of the minds of the greatest men of one century furnishing the elements of thought to the succeeding age.

Those who reverence Newton should show their reverenco by imitating him in his unwearied and eager search for new truth. He was not satisfied with philosophy as he found it; but, taking the floating theories of his time, he employed his immense intellect in giving them system, character, definiteness, so that his philosophy, partaking of the vigor of his mind, has so long held dominion over the world. Though his name is most intimately associated in the general mind with the theory of gravitation, his labors in this department used but a small portion of his energy. Every subject in the vast range of subjects to which he directed his attention retains the marks of his strength. He is often thought of as a mere mathematician, verifying the ideas of others. Far from it. His originality of mind equalled his mathematical exactness of conception. How eagerly did he seize upon every new truth, how ready was his mind for progress! The contemplation of such a character should prevent us from ever remaining satisfied with ideas to which the least doubt can be attached.

CHAPTER V.

"IN THE CONSTANT OSCILLATION OF THE HUMAN MIND BETWEEN IDEAS AND FACTS, AFTER HAVING FOR A MOMENT TOUCHED THE LATTER, IT SEEMS TO SWING BACK MORE IMPETUOUSLY TO THE FORMER." Whewell.

WE pass from the examination of the very minute and of the far-extended, to the common facts of our daily observation; gladly throwing down the telescope and microscope, we will look with the naked eye at nature in the ordinary range of vision.

Were we to select one class of facts to illustrate the ideas we present, and to disprove the attraction of matter, it would be that which relates to oscillatory motion, the action of the pendulum and kindred movements.

The swing of a pendulum, increasing in velocity in proportion to the decrease of distance from the centre of oscillation, the force of its motion being measurable by the area of the circle of which it describes a segment, shows that the nature of force is the same, however its energies may operate. It brings to the mind the relative speed of the planets, increasing as the diameter of their orbits diminishes. Its regular beats mark time with the same precision as does the harmonic motion of the heavenly bodies. It is, therefore, a free, unrestrained movement, showing the laws. of force, and had it been rightly understood, the laws which

regulate the planetary movements might have been distinctly inferred from it. "We feel," says Bailly, in his History of Astronomy, "that nature is very simple in her operations ; the positions and motions of the planets offer at first sight the appearance of intricacy, but the principle which impels them has a naturalness and simplicity like the character of truth;" and this principle has application not only to them, but to all natural and unrestrained motion. Thus in the pendulum, its orbit prescribed and a uniform force of impulse given, motion ensues, invariable, equal, measured by the area described.

A pendulum beating seconds does not change as to time of vibration with the addition or subtraction of weight, nor with a stronger or weaker impulse given to it; the weight of the mass moved and the length of the sweep do not change the time, if the same length of rod is retained. The force of motion is ever in proportion to the mass, and the stronger impulse only increases the range of motion with an increase of velocity that gives the equal time. The impulse lifts it higher and it falls with greater rapidity, and the fall both in distance and velocity determines the succeeding rise. It is evident, therefore, that this result is produced by the same principle which occasions the fall of bodies to the earth; for the downward force is just the force of a body falling vertically the same distance, and the rise is also the samo both in relation to distance and velocity. It is the same principle which causes the rise and fall of a stone thrown into the air, to be in equal times. How can this equal rise and fall of the pendulum be explained on the theory of gravitation? Where is the reference to the centre of attraction, where the gravitating power? How is it that the power drawing to the earth draws and repels