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to which our experience was limited, the fact was yet consistent with the whole analogy of nature. Supposing, then, this power, when extended to the moon, to decrease at the same rate at which it appeared to do in regard to the planets which revolved around the sun, he next set himself to calculate whether its force, at such a distance from the earth, would in reality be sufficient to retain that satellite in its orbit, and to account for its known rate of motion. Now, this step of the discovery was marked by a very singular circumstance, and one strikingly illustrative of the truly philosophic character of this great man's mind. In the computations which he undertook for the purpose of this investigation, he naturally adopted the common estimate of the magnitude of the earth, which was at that time in use among our geographers and seamen. Indeed, no other then existed for him to adopt: but it was even then known to scientific men, that this estimate was loose and inaccurate. In fact, it allowed only sixty English miles to a degree of latitude, instead of sixty-nine and a half, which is the true measurement. The consequence was that the calculation did not answer; it indicated, in fact, a force of gravity in the moon towards the earth, less by one sixth than that which was necessary to give the rate of motion actually possessed by that satellite. Another might have thought this but a trifling discrepancy, and, in such circumstances, might have taxed his ingenuity to account for it in a variety of ways, so as still to save the beautiful and magnificent theory which it came so unseasonably to demolish. But Newton was too true a philosopher, too single-hearted a lover of truth, for this. In his mind, the refutation was a complete one, and it was admitted as such at once. He had made his calculation with care, although one of its elements was false; it did not present the result it
ought to have done, had his hypothesis been as true as it was brilliant; and, in his own estimation, he was no longer the discoverer of the secret mechanism of the heavens. By an act of self-denial, more heroic than any other recorded in the annals of intellectual pursuit, he dismissed the whole speculation from his mind, even for years. We need hardly state how gloriously this sacrifice was in due time rewarded. Had Newton, instead of acting as he did, obstinately persevered in the partially erroneous path into which he had thus been misled, it is impossible to say into how many additional misconceptions and misstatements he might have been seduced, in order to cover the consequences of his first error; or how much the simplicity of the grand truth which had revealed itself to him, as it were, for a moment in the distance, might have been eventually complicated and disfigured by the vạin imaginations of the very mind which had discovered it. gress of science would, no doubt, at last have swept away all these useless and encumbering fictions; but that honour would, probably, have been reserved for another than Newton. Committed to the maintenance of his adopted errors, and with his mental vision even unfitted in some measure for the perception of the truth, he might in that case have been the last to discern the full brightness of that day, the breaking of which he had been the first to descry. But by keeping his mind unbiassed, he was eventually enabled to verify all, and more than all, he had originally suspected. No other speculator had yet followed him in the same path of conjecture; when, a few years after, upon obtaining more correct data, he repeated his calculation, and found it terminate in the very result he had formerly anticipated. The triumph and delight of that moment can hardly be conceived, when he saw at last that the mighty dis
The procovery was indeed all his own! It is said that such was his agitation as he proceeded, and perceived every figure bringing him nearer to the object of his hopes, that he was at last actually unable to continue the operation, and was obliged to request a friend to conclude it for him.
Another very beautiful example of the way in which some of the most valuable truths of philosophy have been suggested, for the first time, by the simplest incidents of common life, is afforded by Galileo's discovery of the regularity of oscillation in the pendulum. It was while standing one day in the metropolitan church of Pisa, that his attention was first awakened to this most important fact, by observing the movements of a lamp suspended from the ceiling, which some accident had disturbed and caused to vibrate. Now this, or something exactly similar, was a phenomenon which, of course, every one had observed thousands of times before. But yet nobody had ever viewed it with the philosophic attention with which it was on this occasion examined by Galileo. Or if, as possibly was the case, any one had been half unconsciously struck for a moment by that apparent equability of motion which arrested so forcibly the curiosity of Galileo, the idea had been allowed to escape the instant it had been caught, as relating to a matter not worth a second thought. philosopher of Italy (for he had not then reached his twentieth year) saw at once the important applications which might be made of the thought that had suggested itself to him. He took care, therefore, to ascertain immediately the truth of his conjecture by careful and repeated experiment; and the result was the complete discovery of the principle of the most perfect measure of time which we yet possess. How striking a lesson is this for us when we discover, or think we discover, any fact in the economy of nature
which we have reason to believe has not previously been observed! Let it be at least verified and recorded. No truth is altogether barren; and even that which looks at first sight the very simplest and most trivial, may turn out fruitsul in precious results.
It seems, after it is stated and described to us, to have been an exceedingly obvious thought which struck Galileo, when, after having ascertained the regular oscillation of the pendulum, he proposed employing it as a measure of time. Some, indeed, may imagine that there was no such extraordinary merit as is generally supposed even in the grand conjecture of Newton, and that it amounted, after all, merely to the application of a law to the movements of the hea venly bodies, which was already known to affect at least every body in the immediate neighbourhood of the earth. But these things are only simple after they are explained. Slight and transparent as we may think the veil to have been which covered the truths alluded to, and others of a similar nature, immediately before they were detected, it is yet an unquestionable fact that this veil had been sufficient to conceal them, for thousands of years, from the observation of all the world. The phenomenon of a heavy body swinging to and fro from a point of suspension had been familiar to every generation from the very
earliest times; and yet, although men had long been very desirous of possessing an accurate and convenient measure of time, and had resorted in different countries to a great variety of contrivances to attain that object, nobody before Galileo had thought of affecting it by means of the pendulum. And, in the same manner, with regard to the law of gravitation: the fact of all bodies having a tendency to fall to the earth must of course have forced itself upon the attention of the very earliest inhabitants of our globe, every day and hour of their existence. Indeed, the law in nearly
all the generality in which Newton found it, had been promulgated even by the philosophy of ancient Rome and Greece. But yet Newton's application and extension of it had occurred to nobody, not even to Galileo himself, who had not many years before been engaged in investigating the exact amount of its influence, within the field in which alone it had hitherto been supposed to operate. Newton not only applied the law of gravitation to the heavenly bodies; but as the principle, when affecting bodies in the neighbourhood of the earth, was that of a force apparently constant, he had to discover and demonstrate the law of its variation.
But, perhaps, the most striking illustration we can give of the strange manner in which important truths will sometimes hide themselves for a long while from observation, even after science has approached almost so near as to touch them, is to be found in the history of the different discoveries relating to the mechanical properties of the air. The knowledge of its positive weight, or gravity, is as old as the days of Aristotle. Even its elasticity was well known to the ancients; about a century before the birth of Christ, constructed one of whose philosophers, Hero of Alexandria, had, upon that principle the fountain, or jet d'eau, which still goes by his name. The common suction-pump is a still older invention, the effect of which, depending, as it does, entirely on the pressure of the atmosphere, might have suggested the true philosophy of that subject, it may be thought, to some one of its innumerable observers. But, in reality, although all the while the air was known to be really a heavy body, nobody for two thousand years found out the true reason why, on its removal from the barrel of the pump by the elevation of the piston, the water rose into the vacant space. The unlearned multitude attributed the phenomenon to a suction, or