Sir Isaac Newton's Life
William Stukeley, M.D., F.R.S. (1752)
Being some account of his family;
& chiefly of the junior part of his life.
In magnis, voluisse sat est.
on 15 April 1726 I paid a visit to Sir Isaac, at his lodgings in Orbels buildings, Kensington: din'd with him, & spent the whole day with him, alone. I acquainted him with my intentions of retiring into the country; & had pitchd on Grantham. I had a brother there in business, who had a family. he had been apprentice to Mr Chrichloe apothecary there, a great acquaintance, & schoolfellow of Sir Isaacs.
Sir Isaac expressed an approbation of my purpose: & especially for Grantham, which is near the place of his nativity: & where he went to the grammar school. he said, he had frequently thought of spending the last of his days, in that very place: and charg'd me, if that house to the east of the church, could now be purchasd at any reasonable price, that I should do it immediately in his name, & he would answer the demand. that house had belong'd to the family of the Skipwith's. he said his old acquaintance Mrs Vincent lived there & a few more, whom he knew.
after dinner, the weather being warm, we went into the garden, & drank thea under the shade of some appletrees, only he, & myself. amidst other discourse, he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. "why should that apple always descend perpendicularly to the ground," thought he to him self: occasion'd by the fall of an apple, as he sat in a comtemplative mood: "why should it not go sideways, or upwards? but constantly to the Earths centre? assuredly, the reason is, that the Earth draws it. there must be a drawing power in matter. & the sum of the drawing power in the matter of the Earth must be in the Earths center, not in any side of the Earth. therefore dos this apple fall perpendicularly, or toward the center. if matter thus draws matter; it must be in proportion of its quantity. therefore the apple draws the Earth, as well as the Earth draws the apple."
That there is a power like that we here call gravity which extends its self thro' the universe & thus by degrees, he began to apply this property of gravitation to the motion of the Earth, & of the heavenly bodys: to consider thir distances, their magnitudes, thir periodical revolutions: to find out, that this property, conjointly with a progressive motion impressed on them in the beginning, perfectly solv'd thir circular courses; kept the planets from falling upon one another, or dropping all together into one center. & thus he unfolded the Universe. this was the birth of those amazing discoverys, whereby he built philosophy on a solid foundation, to the astonishment of all Europe.
Newton's Life at Cambridge
John Conduitt (ca. 1728)
In the year  he retired again from Cambridge on acct of the plague to his mother [in] Lincolnshire & whilst he was musing in a garden it came into his thought that the same power of gravity (wch made an apple fall from the tree to the ground) was not limited to a certain distance from the Earth but that this power must extend much farther than was usually thought — Why not as high as the Moon said he to himself & if so that must influence her motion & perhaps retain her in her orbit, whereupon he fell a calculating what would be the effect of that supposition but being absent from books & taking the common estimate in use among Geographers & our sea men before Norwood had measured the Earth, that 60 English miles were contained in one degree of latitude his computation did not agree with his Theory & inclined him then to entertain a notion that together with the power of gravity there might be a mixture of that force which the moon would have if it was carried along in a vortex, but when the Tract of Picard of the measure of the Earth came out shewing that a degree was about 69½ English miles He began his calculation a new & found it perfectly agreable to his Theory–
A View of Isaac Newton's Philosophy
Henry Pemberton (1728)
The first thoughts, which gave rife to his Principia, he had, when he retired from Cambridge in 1666 on account of the plague. As he sat alone in a garden, he fell into a speculation on the power of gravity: that as this power is not found sensibly diminished at the remotest distance from the center of the Earth, to which we can rise, neither at the tops of the loftiest buildings, nor even on the summits of the highest mountains, it appeared to him reasonable to conclude, that this power must extend much farther than was usually thought; why not as high as the moon, said he to himself? and if so, her motion must be influenced by it; perhaps she is retained in her orbit thereby. However, though the power of gravity is not sensibly weakened in the little change of distance, at which we can place our selves from the center of the Earth; yet it is very possible, that so high as the moon this power may differ much in strength from what it is here. To make an estimate what might be the degree of this diminution, he considered with himself, that if the moon be retained in her orbit by the force of gravity, no doubt the primary planets are carried round the Sun by the like power. And by comparing the periods of the several planets with their distances from the Sun, he found, that if any power like gravity held them in their courses, its strength must decrease in the duplicate proportion of the increase of distance. This he concluded by supposing them to move in perfect circles concentrical to the Sun, from which the orbits of the greatest part of them do not much differ. Supposing therefore the power of gravity, when extended to the moon, to decrease in the same manner, he computed whether that force would be sufficient to keep the moon in her orbit. In this computation, being absent from books, he took the common estimate in use among geographers and our seamen, before Norwood had measured the Earth, that 60 English miles were contained in one degree of latitude on the surface of the Earth. But as this is a very faulty supposition, each degree containing about 69½ of our miles, his computation did not answer expectation; whence he concluded, that some other cause must at least join with the action of the power of gravity on the moon. On this account he laid aside for that time any farther thoughts upon this matter. But some years after, a letter which he received from Dr. Hook, put him on inquiring what was the real figure, in which a body let fall from any high place descends, taking the motion of the Earth round its axis into consideration. Such a body, having the same motion, which by the revolution of the Earth the place has whence it falls, is to be considered as projected forward and at the same time drawn down to the center of the Earth. This gave occasion to his resuming his former thoughts concerning the moon; and Picart in France having lately measured the Earth, by using his measures the moon appeared to be kept in her orbit purely by the power of gravity and consequently, that this power decreases as you recede from the center of the Earth in the manner our author had formerly conjectured. Upon this principle he found the line described by a falling body to be an ellipsis, the center of the Earth being one focus. And the primary planets moving in such orbits round the Sun, he had the satisfaction to see, that this inquiry, which he had undertaken merely out of curiosity, could be applied to the greatest purposes. Hereupon he composed near a dozen propositions relating to the motion of the primary planets about the Sun. Several years after this, some discourse he had with Dr. Halley, who at Cambridge made him a visit, engaged Sir ISAAC NEWTON to resume again the consideration of this subject; and gave occasion to his writing the treatise which he published under the title of mathematical principles of natural philosophy. This treatise, full of such a variety of profound inventions, was composed by him from scarce any other materials than the few propositions before mentioned, in the space of one year and an half.
Lettres sur les Anglois
Letters on the English
François Marie Arouet de Voltaire
François Marie Arouet de Voltaire
Lettre XV: Sur l'Attraction
Letter XV: On Attraction
Ayant par toutes ces raisons, & par beaucoup d'autres encore renversé les tourbillons du Cartésianisme, il desesperoit de pouvoir connoitre jamais, s'il y a un principe secret dans la nature, qui cause à la fois le mouvement de tous les corps célestes & qui fait la pesanteur sur la Terre. S'étant retiré en 1666. à cause de la peste, à la campagne près de Cambridge, un jour qu'il se promenoit dans son jardin, & qu'il voyait des fruits tomber d'un arbre, il se laissa aller à une méditation profonde sur cette Pesanteur dont tous les philosophes ont cherchéz si long tems la cause en vain, & dans laquelle le vulgaire ne soupçonne pas même de mystére; il se dit à lui même, de quelque hauteur dans nôtre hemisphére que tombassent ces corps, leur chûte seroit certainement dans la progression découverte par Galilée; & les espaces parcourus par eux seroient come les quarrez des tems. Ce pouvoir qui fait descendre les corps graves, est le même sans aucune diminution sensible à quelque profondeur qu'on soit dans la terre, & sur la plus haute montagne; pourquoi ce pouvoir ne s'étendroit-il pas jusqu'à la lune? Et s'il est vrai qu'il penétre jusques-là, n'y a t'il pas grande apparence que ce pouvoir la retient dans son orbite & détermine son mouvement? Mais si la lune obeït à ce principe tel qu'il soit, n'est-il pas encore trés raisonable de croire que les autres planétes y sont également soumises? Having by these and several other arguments destroyed the Cartesian vortices, he despaired of ever being able to discover whether there is a secret principle in nature which, at the same time, is the cause of the motion of all celestial bodies, and that of gravity on the Earth. But being retired in 1666, upon account of the Plague, to a solitude near Cambridge; as he was walking one day in his garden, and saw some fruits fall from a tree, he fell into a profound meditation on that gravity, the cause of which had so long been sought, but in vain, by all the philosophers, whilst the vulgar think there is nothing mysterious in it. He said to himself, that from what height soever in our hemisphere, those bodies might descend, their fall would certainly be in the progression discovered by Galileo; and the spaces they run through would be as the square of the times. Why may not this power which causes heavy bodies to descend, and is the same without any sensible diminution at the remotest distance from the centre of the Earth, or on the summits of the highest mountains, why, said Sir Isaac, may not this power extend as high as the moon? And in case its influence reaches so far, is it not very probable that this power retains it in its orbit, and determines its motion?