The Life of Sir Isaac Newton

by David Brewster

In the second[109] letter, he admits that the spherical mass formed by the aggregation of particles would affect the figure of the space in which the matter was diffused, provided the matter descends directly downwards to that body, and the body has no diurnal rotation; but he states, that by earthquakes loosening the parts of this solid, the protuberance might sink a little by their weight, and the mass by degrees approach a spherical figure. He then proceeds to correct an error of Dr. Bentley’s in supposing that all infinites are equal. He admits that gravity might put the planets in motion, but he maintains that, without the Divine power, it could never give them such a circulating motion as they have about the sun, because a proper quantity of a transverse motion is necessary for this purpose; and he concludes that he is compelled to ascribe the frame of this system to an intelligent Agent.

The third letter contains opinions confirming or correcting several positions which Dr. Bentley had laid down, and he concludes it with a curious examination of the opinion of Plato, that the motion of the planets is such as if they had been all created by God in some region very remote from our system, and let fall from thence towards the sun, their falling motion being turned aside into a transverse one whenever they arrived at their several orbits. Sir Isaac shows that there is no common place such as that conjectured by Plato, provided the gravitating power of the sun remains constant; but that Plato’s affirmation is true if we suppose the gravitating power of the sun to be doubled at that moment of time when they all arrive at their several orbits. “If we suppose,” says he, “the gravity of all the planets towards the sun to be of such a quantity as it really is, and that the motions of the planets are turned upwards, every planet will ascend to twice its height from the sun. Saturn will ascend till he be twice as high from the sun as he is at present, and no higher; Jupiter will ascend as high again as at present, that is, a little above the orb of Saturn; Mercury will ascend to twice his present height, that is, to the orb of Venus; and so of the rest; and then, by falling down again from the places to which they ascended, they will arise again at their several orbs with the same velocities they had at first, and with which they now revolve.

“But if so soon as their motions by which they revolve are turned upwards, the gravitating power of the sun, by which their ascent is perpetually retarded, be diminished by one-half, they will now ascend perpetually, and all of them, at all equal distances from the sun, will be equally swift. Mercury, when he arrives at the orb of Venus, will be as swift as Venus; and he and Venus, when they arrive at the orb of the earth, will be as swift as the earth; and so of the rest. If they begin all of them to ascend at once, and ascend in the same line, they will constantly, in ascending, become nearer and nearer together, and their motions will constantly approach to an equality, and become at length slower than any motion assignable. Suppose, therefore, that they ascended till they were almost contiguous, and their motions inconsiderably little, and that all their motions were at the same moment of time turned back again, or, which comes almost to the same thing, that they were only deprived of their motions, and let fall at that time, they would all at once arrive at their several orbs, each with the velocity it had at first; and if their motions were then turned sideways, and at the same time the gravitating power of the sun doubled, that it might be strong enough to retain them in their orbs, they would revolve in them as before their ascent. But if the gravitating power of the sun was not doubled, they would go away from their orbs into the highest heavens in parabolical lines.”[110]

In the fourth letter[111] he states, that the hypothesis that matter is at first evenly diffused through the universe is in his opinion inconsistent with the hypothesis of innate gravity without a supernatural power to reconcile them, and therefore it infers a Deity. “For if there be innate gravity, it is impossible now for the matter of the earth and all the planets and stars to fly up from them, and become evenly spread throughout all the heavens without a supernatural power; and certainly that which can never be hereafter without a supernatural power, could never be heretofore without the same power.”

These letters, of which we have endeavoured to give a brief summary, will well repay the most attentive perusal by the philosopher as well as the divine. They are written with much perspicuity of language and great power of thought, and they contain results which incontestably prove that their author was fully master of his noblest faculties, and comprehended the profoundest parts of his own writings.[112]

The logical acuteness, the varied erudition, and the absolute freedom from all prejudice which shine throughout the theological writings of Newton, might have protected them from the charge of having been written in his old age, and at a time when a failure of mind was supposed to have unfitted him for his mathematical investigations. But it is fortunate for his reputation, as well as for the interests of Christianity, that we have been able to prove the incorrectness of such insinuations, and to exhibit the most irrefragable evidence that all the theological writings of Newton were composed in the vigour of his life, and before the crisis of that bodily disorder which is supposed to have affected his reason. The able letters to Dr. Bentley were even written in the middle of that period when want of sleep and appetite had disturbed the serenity of his mind, and enable us to prove that this disturbance, whatever was its amount, never affected the higher functions of his understanding.

When a philosopher of distinguished eminence, and we believe not inimical to the Christian faith, has found it necessary to make a laboured apology for a man like Newton writing on theological subjects, and has been led to render that apology more complete by referring this class of his labours to a mind debilitated by age and weakened by its previous aberrations, it may be expected from an English biographer, and one who acknowledges the importance of revealed truth, and the paramount interest of such subjects above all secular studies, to suggest the true origin of Newton’s theological inquiries.

When a mind of great and acknowledged power first directs its energies to the study of the material universe, no indications of order attract his notice, and no proofs of design call forth his admiration. In the starry firmament he sees no bodies of stupendous magnitude, and no distances of immeasurable span. The two great luminaries appear vastly inferior in magnitude to many objects around him, and the greatest distances in the heavens seem even inferior to those which his own eye can embrace on the surface of the earth. The planets, when observed with care, are seen to have a motion among the fixed stars, and to vary in their magnitude and distances, but these changes appear to follow no law. Sometimes they move to the east, sometimes to the west, sometimes towards the north, and sometimes towards the south, and at other times they are absolutely stationary. No system, in short, appears, and no general law seems to direct their motions. By the observations and inquiries of astronomers, however, during successive ages, a regular system has been recognised in this chaos of moving bodies, and the magnitudes, distances, and revolutions of every planet which composes it has been determined with the most extraordinary accuracy. Minds fitted and prepared for this species of inquiry are capable of understanding the great variety of evidence by which the truth of the planetary system is established; but thousands of individuals who are even distinguished in other branches of knowledge are incapable of such researches, and view with a skeptical eye the great and irrefragable truths of astronomy.

That the sun is stationary in the centre of our system,—that the earth moves round the sun, and round its own axis,—that the earth is 8000 miles in diameter, and the sun one hundred and ten times as large,—that the earth’s orbit is 190 millions of miles in breadth,—and that if this immense space were filled with light, it would appear only like a luminous point at the nearest fixed star,—are positions absolutely unintelligible and incredible to all who have not carefully studied the subject. To millions of our species, then, the great book of nature is absolutely sealed, though it is in the power of all to unfold its pages, and to peruse those glowing passages which proclaim the power and wisdom of its mighty Author.

The book of revelation exhibits to us the same peculiarities as that of nature. To the ordinary eye it presents no immediate indications of its Divine origin. Events apparently insignificant—supernatural interferences seemingly unnecessary—doctrines almost contradictory—and prophecies nearly unintelligible occupy its pages. The history of the fall of man—of the introduction of moral and physical evil—the prediction of a Messiah—the actual advent of our Saviour—his instructions—his miracles—his death—his resurrection—and the subsequent propagation of his religion by the unlettered fishermen of Galilee, are each a stumbling block to the wisdom of this world. The youthful and vigorous mind, when first summoned to peruse the Scriptures, turns from them with disappointment. It recognises in them no profound science—no secular wisdom—no Divine eloquence—no disclosures of nature’s secrets—no direct impress of an Almighty hand. But, though the system of revealed truth which this book contains is, like that of the universe, concealed from common observation, yet the labours of centuries have established its Divine origin, and developed in all its order and beauty the great plan of human restoration. In the chaos of its incidents we discover the whole history of our species, whether it is delineated in events that are past or shadowed forth in those which are to come,—from the creation of man and the origin of evil, to the extinction of his earthly dynasty and the commencement of his immortal career.