was revived a few years ago, and acquired notoriety at the expense of Newton and Halley’s fame. It fell to the lot of Mr. Baily to discover a large number of his letters in private hands, with others, and a manuscript autobiography, upon the shelves of the library in the observatory; and, upon their publication in 1835, by order of the Lords Commissioners of the Admiralty, some painful and unexpected disclosures were made. It may be admitted that Flamstead exaggerates his own case, that his temper was irascible, that he did not appreciate the value of Newton’s theory, and over-estimated the importance of his own labors; yet, after having allowed these elements of correction full force, the conclusion is sufficiently plain, that he was most injuriously treated, and that much of the moral distinction with which posterity has crowned the head of Newton, is altogether misplaced. His deep obligations to Flamstead’s lunar observations are acknowledged in the first edition of the Principia, but carefully suppressed in the second, apparently when vindictive feeling had begun to operate; and, in fact, nothing is more remarkable than the opinion universally entertained of the meek and placable disposition of the great philosopher, and the want of temper and honor displayed in his dealings with Flamstead. The truth appears to be, that as when we view a country beneath a brilliant sky and a balmy atmosphere, we are apt to frame our impressions of the people in harmony with the beauty of the scene; so, to the early admirers of Newton, his intellectual greatness invested with fictitious lustre his private character, and the infirmities of the man were lost sight of in the glory of the sage.
But however much we may take from the moral greatness usually attributed to Newton—and a considerable abatement is unquestionably necessary—his reputation for wonderful sagacity and grasp of mind is incapable of impeachment. The course of events has only served to render more conspicuous that sublime intelligence by which he unraveled the mechanism of the heavens, and establish more indisputably his claim to be regarded as the architect of physical astronomy. To determine the motions of the heavenly bodies was the work of Keppler: to explain and demonstrate the causes of those motions was the achievement of Newton. So far, however, from gaining universal assent when first proposed, his theory was ill understood, slightly appreciated, or altogether rejected by numbers of scientific men; and—especially on the continent—it very slowly won its way to notice and confidence. Newton survived the publication of the Principia forty years, and at the time of his death—according to Voltaire—it had not twenty readers out of the country of its production. It was not until the mutual perturbations of the planets began to occupy the attention of the continental philosophers, that his theory was fully admitted abroad, and the work in which it was developed took the rank it has since occupied, preëminent—in the words of Laplace—above all the productions of the human mind. It is a common, but vulgar error, to suppose the merit of our countryman to lie in conceiving the idea of the attraction of gravitation. That idea had been suggested to many minds long before his time, and the impression had been created that such a power in nature was the cause of the planetary motions. Thus Keppler surmised an attractive force to reside in the sun, producing these movements; and he even threw out the conjecture that this force diminishes in proportion to the square of the distance of the body on which it was exerted. Borelli and Hooke, also, distinctly developed the influence of gravity; and both referred the orbits of the planets to the doctrine of attraction combining with their own proper motions to produce curvilinear movements. What really distinguished Newton, was not the idea of gravity as the principle of attachment between the different members of the solar system, but proving it to be so. He succeeded vague surmise upon the point with mathematical demonstration: explained and applied the laws of the force—an accomplishment which crowns him with honor above all his rivals; inasmuch as he who works a mine, and distributes its wealth through society, is incomparably in advance of him who has merely apprehended its existence, but failed in gaining access to its treasures.
The manor-house of Woolsthorpe, a few miles from Grantham, seated in a little valley near the source of the Witham, was the scene of Newton’s birth. Popular tradition reports, that the fall of an apple from a tree, in the orchard belonging to this house, was the mustard-seed out of which ultimately grew the grand theory of universal gravitation, and the story is not without a leaven of truth. It is certain that, to avoid the plague which ravaged England in 1666, Newton retired from Cambridge; and, when sitting alone, in his garden at Woolsthorpe, his thoughts were directed to that remarkable power which causes all bodies to descend toward the centre of the earth. The supposition presented itself, that as this power extends to the highest altitudes of the earth’s surface, it probably extends much farther into space; so that even the moon may gravitate toward the earth, and be balanced in her orbit by the combined force of attraction and the centrifugal force implied in her motion. If this were true, the planets might be supposed to gravitate toward the sun, and to be restrained thereby from flying off under the action of the centrifugal force. Sixteen years rolled away before this beautiful hypothesis was verified, and difficulties arose in testing it, which seemed to disprove it altogether. It was necessary to calculate the force of gravity at the surface of the earth; to estimate its diminished energy at an increased distance; and, after having found the law of the diminution, to ascertain whether the phenomena of the lunar motions corresponded proportionably with those of falling bodies at the terrestrial surface. Assuming the force of gravity to vary inversely as the square of the distance, it followed that, at the distance of the moon, it would be about 3600 times less than at the surface of the earth. The problem, therefore, to be solved was, whether the versed sine of an arc described by the moon—which measures the space through which in the same time she would fall to the earth, if abandoned to the action of gravity—would be 3600 times less than the space through which in the same time a heavy body falls, at the earth’s surface,
A B being the arc of the moon’s orbit, c d the sine of the arc, and e f the versed sine. After a careful study of the lunar observations supplied by Flamstead, and a series of calculations—displaying unexampled originality and industry—Newton fully demonstrated that the versed sine of an arc described by the moon in one minute, was equal to the space traversed in descent by a heavy body at the surface of the earth in one second—the exact proportion that ought to exist, according to the modification to which the intensity of gravity is subject by variation of distance.
The first certain gleam of this grand conclusion obtained by Newton, is said so to have overpowered him, that he was obliged to suspend his calculations, and call in the aid of a friend, to finish the last few arithmetical computations. He saw the important relations of the demonstration—the planets wheeling round the sun—the satellites round the planets—the far wandering comets returning to the source of light in obedience to the law of gravitation: a result sufficient to throw the successful discoverer into nervous excitement. It is clear that, if a body be projected into space, it will proceed in the direction of the original impulse, and with a uniform velocity, forever—supposing no obstacle to impede its course. But the combination of two antagonistic forces will produce a resulting motion in a diagonal direction.
Suppose the straight lines A B, to represent the direction in which the earth would travel under the influence of the projectile force, which launched it into universal space: the straight lines A S, are those it would describe at any point of its orbit, if surrendered to the influence of the sun’s attraction. The primitive impulse is, however, checked by the solar attraction, and the latter by the former; so, that while the earth—if abandoned to either—would describe A B, or A S, the effect of their joint influence incessantly acting is to deflect it from both, and produce a curved path. The cause perpetually operating, the effect is constant—and hence the formation of the terrestrial orbit; and the cause extending to the other bodies in the system, the planetary orbs are deflected from their natural rectilinear paths, and pursue a circuit round the common centre. The force of attraction is, however, proportional to the quantity of matter, and the proximity of the attracting body. Like light, the power of gravitation is weakened by diffusion, and diminishes as the square of the distance increases. This square is the product of a number multiplied by itself. A planet, therefore, twice our distance from the sun, will gravitate four times less than we do—the product of two multiplied by itself being four. Such is the great Law of Gravity, subject to the two conditions, that its force is directly as the mass of the bodies, and inversely as the square of the distance. It extends to the confines of the system, and acts as a mighty invisible chain to keep the primary bodies in brotherly relationship to each other, and in mutual subjection to the central luminary. And who can trace its operation without recognizing a Supreme Potentate, who appointed to the sun his place, launched the planets in the depths, obedient to a law which has preserved the family compact—originally established—unbroken through the long series of ages.
It must, however, be borne in mind that the attraction between bodies is mutual, proportioned to their masses and distances. While the sun attracts the planets toward himself, they also attract the sun, though their effect is comparatively small, owing to the vastness of the solar mass. The planets likewise act upon each other; and as their relative distances are perpetually varying, certain perturbations are caused in the system, which, though minute in each particular case, become considerable by accumulation, and yet are ultimately corrected and repaired by the same cause that produces them. Newton left to posterity the task of thoroughly investigating these inequalities, of showing them to be a result of the law of gravitation, and establishing the permanence of the system, notwithstanding the accumulating influence of its internal disturbances. He himself had no gleam of the latter truth, but seems to have entertained an opinion that the irregularities occasioned by the mutual action of the planets and comets would probably go on increasing till the system either wrought out its own destruction or received reparation from the direct intervention of its Creator. But Euler, Clairaut, D’Alembert, Lagrange, and Laplace, have demonstrated the problem that the perturbations of the planets are periodic in their nature, that accurate compensation for them is laid up in store, so that the system is not arranged upon a principle of self-destruction. The elements of disorder and decay are removed from it. The very conditions of its existence guarantee its stability till the will of the great Ruler shall be expressed to the contrary. When an end shall come to its present constitution, that will not be the effect of its own faulty architecture, but of the fiat of Omnipotence.