Page:Lettersconcerni01conggoog.djvu/175

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150
Letters concerning

vex on one ſide and flat on the other, in caſe the flat Side be turn'd towards the Object, the Error which ariſes from the Conſtruction and Poſition of the Glaſs, is above five thouſand Times leſs than the Error which ariſes from the Refrangibility: And therefore, that the Shape or Figure of the Glaſſes is not the Cauſe why Teleſcopes cannot be carried to a greater Perfection, but ariſes wholly from the Nature of Light.

For this Reaſon he invented a Teleſcope, which diſcovers Objects by Reflection and not by Refraction. Teleſcopes of this new kind are very hard to make, and their Uſe is not eaſy. But according to the Engliſh, a reflective Teleſcope of but five Feet, has the ſame Effect as another of an hundred Feet in Length.

LETTER