me the more. I have difcover'd a new Property of Matter, one of the Secrets of the Creator; and have calculated and discover'd the Effects of it. After this fhall People quarrel with me about the Name I give it.

VORTICES may be call'd an occult Quality because their Existence was never prov'd: Attraction on the contrary is a real Thing, because its Effects are demonftrated, and the Proportions of it are calculated. The Caufe of this Caufe is among the Arcana of the Almighty.

Procedes buc, & non amplius.

Hither thou fhalt go, and no farther.

LETTER

LETTER XVI.

ON

Sir Isaac Newton's

OPTICK S.

T

HE Philofophers of the laft Age found out a new Univerfe; and a Circumftance which made its Discovery more difficult, was, that no one had so much as fufpected its Existence. The moft Sage and Judicious were of Opinion, that 'twas a frantic Rashness to dare fo much as to imagine that it was poffible to guess the Laws by which the celestial Bodies move, and the manner how Light acts.

Gali

leo

leo by his aftronomical Discoveries, Kepler by his Calculation, Des Cartes (at leaft in his Dioptricks) and Sir Ifaac Newton in all his Works, feverally faw the Mechanism of the Springs of the World. The Geometricians have subjected Infinity to the Laws of Calculation. The Circulation of the Blood in Animals, and of the Sap in Vegetables, have chang'd the Face of Nature with regard to us. A new kind of Existence has been given to Bodies in the AirPump. By the Affiftance of Telescopes Bodies have been brought nearer to one another. Finally, the feveral Discoveries which Sir Ifaac Newton has made on Light, are equal to the boldest Things which the Curiofity of Man could expect, after fo many philofophical Novelties.

TILL Antonio de Dominis, the Rainbow was confider'd as an inexplicable Miracle. This Philofopher guess'd that it was a neceffary Effect of the Sun and Rain. Des Cartes gain'd immortal Fame, by his mathematical Explication of this

fo

fo natural a Phænomenon. He calculated the Reflexions and Refractions of Light in Drops of Rain; and his Sagacity on this Occafion was at that Time look'd upon as next to divine.

BUT what would he have faid had it been prov'd to him that he was mitaken in the Nature of Light; that he had not the leaft Reafon to maintain that 'tis a globular Body: That 'tis falfe to affert, that this Matter spreading it felf through the whole, waits only to be projected forward by the Sun, in or der to be put in Action, in like Manner as a long Staff acts at one end when push'd forward by the other. That Light is certainly darted by the Sun; in fine, that Light is tranfmitted from the Sun to the Earth in about feven Minutes, tho' a Cannon Ball, which were not to lose any of its Velocity, cou'd not go that Distance in lefs than twenty five Years. How great wou'd have been his Astonishment, had he been told, that Light does not reflect directly by impinging against the folid Parts of Bo

dies; that Bodies are not transparent when they have large Pores; and that a Man fhould arife, who would demonftrate all these Paradoxes, and anatomize a fingle Ray of Light with more Dexterity than the ableft Artift diffects a human Body. This Man is come. Sir Ifaac Newton has demonftrated to the Eye, by the bare Affiftance of the Prifm, that Light is a Compofition of colour'd Rays, which, being united, form white Colour. A fingle Ray is by him divided into feven, which all fall upon a Piece of Linen, or a Sheet of white Paper, in their Order one above the other, and at unequal Distances. The firft is Red, the fecond Orange, the third Yellow, the fourth Green, the fifth Blue, the fixth Indigo, the seventh a Violet Purple. Each of these Rays transmitted afterwards by an hundred other Prisms, will never change the Colour it bears; in like Manner as Gold, when completely purg'd from its Drofs, will never change afterwards in the Crucible. As a fuperabundant Proof that