What is the measure of perfection in the ogan that is to fix the standard? Whose eye, in reference to the objects of vision, is to be taken as a standard? Does not this sense vary in keenness in different individuals? But even if a standard were obtained in the unaided organ, yet the happy direction of art may carry the range of its powers still further, as in the application of the lens to the eye, and then another standard is to be assumed. And may not invention proceed still further, and then where will the series of standards end? Has it happened that the true knowledge of things has been obtained by the senses alone? Their assistance is not disputed. Would astronomy have ever advanced to that perfect state it now presents (and man, who boasts of his intellect, may well reflect with exultation on its progress) if Copernicus and other great astronomers had limited their pursuits to the bare notice of the celestial bodies,
