LETTER VII.

OF THE NEWTONIAN SYSTEM, AND DISCOVERIES.

IN all ages of the world, mankind in general have been nearly the same: the powers of the mind are various; but there are certain prescribed bounds which it is the lot of but few to pass. The multitude were certainly designed for manual labour and industry, and their minds are, by custom, made conformable to their employments. Intent upon the common concerns and business of life, they have but little leisure, and less inclination, for mental improvement. This is the wise designation of Providence. The earth must be cultivated to support its inhabitants; a general refinement would be as prejudicial as a general barbarity.

Humanity, however, has higher privileges. Arts and sciences, legislation and morals, are absolutely necessary to the due regulation and order of civil society. And that a knowledge of them may be properly distributed, the Author of Nature has, at different times, raised up some great and illus trious genius to enlighten and instruct us. In religion, our most momentous concern, he has condescended to give us a divine guide; and in every art and science, we have had preceptors of eminence proportionate to the importance of the subject. Every thing bears the marks of omniscience: wherever we turn our eyes, we perceive a presiding intelligence, that informs and regulates the whole. To enumerate the most shining characters of the

H

kind here mentioned, and to show the discriminating excellence and utility of the several pursuits in which they were engaged, would be a matter of much difficulty, and foreign to our purpose. The subject upon which we are, at present, to employ our attention, is physical astronomy; and we are now to consider the genius and doctrines of a man, who, in his philosophical character, appears to have been endowed with superior faculties, in order to dissipate the accumulated mists of ignorance and error, and to lead us to a knowledge of those truths, which the wisdom of ages had been unable to discover.

The person to whom we owe these obligations, is the illustrious Newton, who was born at Wolstrop in Lincolnshire, on Christmas-day 1642. His father was the reduced descendant of a noble family; but the genius of his son eclipsed all the splendor of hereditary titles and honours. Of his juvenile studies we have but little knowledge, none of his first attempts, or essays, having ever appeared. He seems to have been an inventor rather than a student; and to have entered at once into the depths of science, without attending to the usual gradations. It was on this account that Fontenelle applied to him the following idea of the ancients, concerning the unknown source of the majestical river that fertiles Egypt: Il n'a pas été permis aux hommes de voir le Nil foible et nais

sant.

Every science upon which this great man employed his attention, received a new form from his

hands, and was carried to a degree of perfection unlooked for by the ancients. In the course of a few years he had destroyed the works of ages, and erected an edifice of his own, which will be as durable as the fabric of nature itself. Algebra, geometry, mechanics, optics, chronology, philosophy and astronomy, began now to assume an unusual splendor and dignity; and by his improvements and discoveries, were rendered prodigiously more extensive and important. The method of Fluxions, in particular, was entirely his own invention; which alone was sufficient to have rendered his name immortal. The exquisite subtilty of this doctrine is such, that the powers of the human mind seem inadequate to a higher pursuit. Any thing beyond it, must be the science of pure intelligence.

From a genius like this, what had we not to expect? His account of the universe, and the laws by which it is regulated, is founded upon the most indubitable principles of reason, science, and observation. We are no longer compelled to wander through the intricate mazes of hypothesis and conjecture. Nature appears again in all her primitive simplicity. Newton has dissolved the chaos, and separated the light from the darkness. His inimitable work, The Mathematical Principles of Natural Philosophy, contains the true astronomical faith, which may be strengthened and improved by farther enquiries, but can never be shaken or destroyed.

To give a perspicuous and methodical account

of his various investigations and discoveries, would be a work of great difficulty, and what, from the incompetency of your present acquirements, could afford you but little instruction. Confining myself, therefore, to those which are the most familiar and interesting, I shall begin with his speculations upon gravity and attraction, and relate from the authority of his commentator and friend, Dr. Pemberton, the simple incident which is said to have given birth to them.

About the year 1666, or the twenty-fourth year of his age, he retired from Cambridge into the country, in order to avoid the plague, which, at that time, raged with great violence; and sitting one day in an orchard, an apple, by chance, falling from one of the trees, caused him to enter into a number of reflections. The phænomena of falling bodies particularly engaged his attention; and pursuing the ideas which presented themselves to his mind, he carried his researches from the earth to the heavens, and began to investigate the nature of motion in general. Because there is motion, he observed, there must be a force which produces it; but what is this force? That a body, when left to itself, will fall to the ground, is known to the most illiterate; but if you ask them the reason of its doing so, they will consider you either a fool or a madman: the circumstance is too common to excite their surprise, although philosophers are so much embarrassed with it, that they find it almost inexplicable.

Let us follow Newton, and examine this ques

tion a little farther.

Does the cause of weight or

gravity exist in the bodies themselves, or out of them? It seems natural to conclude, that the propensity which all suspended bodies have of falling to the earth, exists in the bodies themselves. When I take a stone, and let it drop from my hand, it falls immediately to the ground; and would fall still farther, if there were a hole in the earth, and nothing prevented its passage. And the same thing happens to all other bodies, with which we are acquainted there is no material substance, either great or small, but what will fall towards the earth the moment it is disengaged, and free from all outward impediments.

In like manner it may be observed, that when a stone or any other body is placed upon a table, it presses the table with the same force, by which it would, if left to itself, fall to the ground. And when a body is suspended at the end of a string, the force that pushes it downwards stretches the string, and if it is not sufficiently strong, will break it. From which circumstances it plainly appears, that all bodies press with a certain force against the obstacles which support and hinder them from falling; and that the degree of force, in either case, is precisely the same with that, which in a free space would bring them to the ground.

The cause of this propensity in all bodies to fall to the earth, be it what it may, is called gravitation or attraction; and when a substance is said to be heavy, nothing more is meant than the tendency it has to fall to the ground; or the force by