Visual Education (Jan-Nov 1920)

Human Eyes and Optical Instruments. Editor's Note — This article is the first of a series by Dr. Moulton on Human Eyes and Optical Instruments. The one published in this issue is limited to a consideration of eyes without optical aid. Later ones will take up the whole range of ordinary optical instruments and illustrations will be given of the wonders which they reveal. THE higher forms of animals possess five senses through which they have contact with the external world. The relative importance of these senses varies from one species to another. In the case of human beings the most valuable sense is undoubtedly that of sight, and the eyes of men are probably better than those of any other animal. Although we human beings learn of the exterior world through all of our senses, we do not get the same amount or exactly the same kind of information from all of them. We learn more through our eyes than through any other sense organs. If it were not so, the impressions we retain after traveling in unfamiliar regions would not be so largely visual. If it were not so, we should not invariably say we had seen a country rather than that we had sensed it in some other way. An additional fact of importance is that our eyes give us information that can be obtained otherwise only with difficulty or not at all. For example, nearly all we know of the size and shape of objects comes from having seen them, especially if they are beyond the reach of our hands; and absolutely all we know of the planets and the millions of stars in the universe beyond this little earth on which we live has been learned through the sense of sight. The importance of this may be judged from the fact that it was from observations of these bodies that the fundamental and very important laws of mechanics were discovered; and, indeed, from the fact that the safe navigation of the seas and the accurate determination of time are even now dependent upon daily astronomical observations. It is, of course, through our eyes alone that we learn of the colors of objects ; that we judge of the progress of ripening fruit or gram ; that we note the glow of health in the cheek, and that we are thrilled by the rainbow's spectrum or the tints of the evening sky. But this, which pertains to the natural eye, is not all, for no other sense has benefited so much from artificial and instrumental aid. If our eyes are defective, glasses will generally correct them. If they fail in accommodation with age, suitable lenses will overcome the difficulty. If they do not gather enough light to enable us to see faint or far distant objects, telescopes will bring them within our view. If they can not discern very minute objects, microscopes will magnify them. If glimpses of things are fleeting, photographs will preserve them. If bodies seem flat in pictures, stereoscopic views will give them the appearance of solidity. If objects appear stationary in pictures, moving pictures will show them in action, in short, the ordinary defects of the eyes can be remedied, the infinite and the infinitesimal can both be brought into range, the scenes of all times and places can be preserved in three dimensions and in motion — indeed, the universe, in both space and time, can be brought to us here and now. But it is not necessary to argue the actual and relative importance of the sense of sight. It is irrefutably established bv the very idioms and imagery 25