ATTRACTION, a general term, used to denote the power or principle by which bodies mutually tend towards each other, without regarding the cause or ac tion that may be the means of producing the effect.
The philosopher Anaxagoras, who lived about 500 years before the Christian xra, is generally considered as the first who noticed this principle as subsisting be tween the heavenly bodies and the earth, which he considered as the centre of their motions. The doctrines of Epicurus and of Democritus are founded on the same opinion.
Nicholas Copernicus appears to have been one of the first among the moderns, who had just notions of this doctrine.
After him, Kepler brought it still near er perfection, having determined that bodies tended to the centres of the larger round bodies of which they formed a part, and the smaller celestial bodies to the great ones nearest to them, instead of to the centre of the universe : he also accounted for the general motion of the tides on the same principle, by the at traction of the moon; and expressly calls it virtus trattoria guar in Luna eat; besides this, he refuted the old doctrine of the schools, "that some bodies were natural ly light, and for that reason ascended, while others were by their nature heavy, and so fell to the ground : declaring that no bodies whatsoever are absolutely light, but only relatively so, and that all matter is subjected to the law of gravitation.
Dr. Gilbert, a physician at London, was the first in this country who adopted the doctrine of attraction ; in the year 1600, he published a work, entitled "De Mag nete Magneticisque Corporibus;" which contains a number of curious things; but he did not sufficiently distinguish be tween attraction and magnetism.
The next after him was Lord Bacon, who, though not a convert to the Coper nican system, yet acknowledged an at tractiVe power in matter.
In France, also, we find Ferinat and Ro herval, mathematicians of great eminence, maintaining the same opinion. The lat ter, in particular, made it the fundamental principle of his system of physical astro nomy, which he published in 1644, under the title of " Arist. Samii de Mundi Sys
tems." Dr. Hooke, however, was the person who conceived the most just and clearno tions of the doctrine of gravitation, of any before Newton, in his work, called " An Attempt to prove the Motion of the Earth :" 1674. He observes, that the hy pothesis on which he explains the system of the world, is in many respects different from all others ; and that it is founded on the following principles 1. That all the heavenly bodies have not only an attrac tion or gravitation towards their own cen tres, lout that they mutually attract each other within the sphere of their activity. 2. That all bodies which have a simple or direct motion continue to move in a right line, if some force operating without in cessantly, does not constrain them to de scribe a circle, an ellipse, or some other more complicated curve. 3. That attrac tion is so much the more powerful, as the attracting bodies are nearer to each other.
But the precise determination of the laws and limits of the doctrine of attrac tion was reserved for the genius of New ton : in the year 1666, he first began to turn his attention to this subject, when, to avoid the plague, he had retired from Lon don into the country ; but, on account of the incorrectness of the measures of the terrestrial meridian, made before this pe riod, he was unable to bring his calcula tions on the subject to perfection at first.
Some years afterwards, his attention was again called to attraction by a letter of Dr. Hooke's ; and Picard having about this time measured a degree of the earth, in France, with great exactness, he em ployed this measure in his calculations, instead of the one he had before used, and found, by that means, that the moon is retained in her orbit by the sole power of gravity, supposed to be reciprocally pro portional to the squares of the distances.