Monsieur Auzout´s judgement touching the apertures of object-glasses, and their proportions, in respect of the several lengths of telescopes

This author, observing in a small French tract lately written by him to a countryman of his, Monsieur L´Abbe Charles; that great optick-glasses have almost never as great an aperture as the small ones, in proportion to what they magnifie, and that therefore they must be more dim; takes occasion to inform the reader, that he hath found, that the apertures, which optick-glasses can bear with distinctness, are in about a subduplicate proportion ti their lengths;