Civilisation and Eyesight

MY attention has only recently been called to a communication from Lord Rayleigh, which appears in NATURE for the 12th inst. (p. 340), and on which I crave permission to make a few observations. Lord Rayleigh questions whether the eyes of savages, "merely as optical instruments," are greatly superior to our own; and suggests that any superiority which savages possess may depend upon "attention and practice in the interpretation of minute indications." He explains that "the resolving power of an optical instrument is limited by its aperture," and then proceeds as follows:-