ction the Art of Increaſing it, and of aſſiſting our Eyes by Teleſcopes can be carried.
Des Cartes, from a noble Confidence, that was very excuſable conſidering how ſtrongly he was fir'd at the firſt Diſcoveries he made in an Art which he almoſt firſt found out; Des Cartes, I ſay, hop'd to diſcover in the Stars, by the Aſſiſtance of Teleſcopes, Objects as ſmall as thoſe we diſcern upon the Earth.
But Sir Iſaac has ſhown, that Dioptric Teleſcopes cannot be brought to a greater Perfection; becauſe of that Refraction, and of that very Refrangibilty, which at the ſame Time that they bring Objects nearer to us, ſcatter too much the elementary Rays; he has calculated in theſe Glaſſes the Proportion of the ſcattering of the red and of the blue Rays; and proceeding ſo far as to demonſtrate Things which were not ſuppos'd even to exiſt, he examines the Inequalities which ariſe from the Shape or Figure of the Glaſs, and that which ariſes from the Refrangibility. He finds, that the object Glaſs of the Teleſcope being con-
