GBANTHAM ADDEE8S. 279 



ceive how near an approach had been made to the calculus 

 before the great event of its final discovery. 



There had in like manner been approaches made to the 

 law of gravitation, and the dynamical system of the universe. 

 Galileo's important propositions on motion, especially on 

 curvilinear motion, and Kepler's laws upon the elliptical 

 form of the planetary orbits, the proportion of the areas to the 

 times, and of the periodic times to the mean distances, 

 and Huygens's theorems on centrifugal force, had been 

 followed by still nearer approaches to the doctrine of attrac- 

 tion. Borelli had distinctly ascribed the motion of satellites 

 to their being drawn towards the principal planets, and thus 

 prevented from being carried off by the centrifugal force.* 



Even the composition of white light, and the different action 

 of bodies upon its component parts, had been vaguely con- 

 jectured by Ant. de Dominis, Archbishop of Spalatro, at the 

 beginning, and more precisely in the middle of the seventeenth 

 century by Marcus (Kronland of Prague), unknown to New- 

 ton, who only refers to the Archbishop's work; while the 

 Treatise of Huygens on light, Grimaldi's observations on 

 colours by inflexion as well as on the elongation of the image 

 in the prismatic spectrum, had been brought to his attention, 

 although much less near to his own great discovery than 

 Marcus's experiment.! 



able approach to the calculus is the rule given to suppress all terms in 

 which the square or the cube of the small quantity is found, because, it is 

 said, those powers are infinitely small in comparison of the first power of 

 the quantity. Thus calling that quantity e (or as we should say d x\ he 

 considers e 2 and e 3 (dx 2 and <Zz 3 ) as to be entirely rejected. Hudde's letter 

 to Schooten, 1658. Descartes' Geom. I. 507. 



* Galileo's problem on the motion of bodies by gravity acting uniformly 

 in parallel lines could have been no novelty to Newton ; and Huygens's 

 explanation of centrifugal tendency by the comparison of a stone's ten- 

 dency to fly off when whirled round in a sling, is as correctly as possible 

 that now received. But his theorems had been investigated by Newton 

 several years before, as appears from a letter of Huygens himself. 



f The Archbishop's explanation in 1611 of the rainbow, and his experi- 

 ment to illustrate it by a thin glass globe filled with water and giving 



