 | XII
NEWTON AND THE LAW OF GRAVITATION
A History of Science: in Five Volumes. Volume II: The Beginnings of Modern Science |  |
PROPOSITION VII., THEOREM VII.
"That there is a power of gravity tending to all bodies, proportional to the several quantities of matter which they contain.
"That all the planets mutually gravitate one towards another we have proved before; as well as that the force of gravity towards every one of them considered apart, is reciprocally as the square of the distance of places from the centre of the planet. And thence it follows, that the gravity tending towards all the planets is proportional to the matter which they contain.
"Moreover, since all the parts of any planet A gravitates towards any other planet B; and the gravity of every part is to the gravity of the whole as the matter of the part is to the matter of the whole; and to every action corresponds a reaction; therefore the planet B will, on the other hand, gravitate towards all the
"Hence it would appear that the force of the whole must arise from the force of the component parts.''
Newton closes this remarkable Book iii. with the following words:
"Hitherto we have explained the phenomena of the heavens and of our sea by the power of gravity, but have not yet assigned the cause of this power. This is certain, that it must proceed from a cause that penetrates to the very centre of the sun and planets, without suffering the least diminution of its force; that operates not according to the quantity of the surfaces of the particles upon which it acts (as mechanical causes used to do), but according to the quantity of solid matter which they contain, and propagates its virtue on all sides to immense distances, decreasing always in the duplicate proportions of the distances. Gravitation towards the sun is made up out of the gravitations towards the several particles of which the body of the sun is composed; and in receding from the sun decreases accurately in the duplicate proportion of the distances as far as the orb of Saturn, as evidently appears from the quiescence of the aphelions of the planets; nay, and even to the remotest aphelions of the comets, if those aphelions are also quiescent. But hitherto I have not been able to discover the cause of those properties of gravity from phenomena, and I
The very magnitude of the importance of the theory of universal gravitation made its general acceptance a matter of considerable time after the actual discovery. This opposition had of course been foreseen by Newton, and, much as be dreaded controversy, he was prepared to face it and combat it to the bitter end. He knew that his theory was right; it remained for him to convince the world of its truth. He knew that some of his contemporary philosophers would accept it at once; others would at first doubt, question, and dispute, but finally accept; while still others would doubt and dispute until the end of their days. This had been the history of other great discoveries; and this will probably be the history of most great discoveries for all time. But in this case the discoverer lived to see his theory accepted by practically all the great minds of his time.
Delambre is authority for the following estimate of Newton by Lagrange. "The celebrated Lagrange,'' he says, "who frequently asserted that Newton was the greatest genius that ever existed, used to add—`and the most fortunate, for we cannot find more than once
God said `Let Newton be!' and all was light.''
| XII
NEWTON AND THE LAW OF GRAVITATION
A History of Science: in Five Volumes. Volume II: The Beginnings of Modern Science | |