Page:The fairy tales of science.djvu/131



old proverb which, heads this chapter is suggestive of many wonderful truths connected with vision. Science has demonstrated that two eyes are better than one, for many reasons. We require two eyes to estimate distances, and to obtain a true idea of the roundness, relief, and solidity of natural objects. Those ugly one-eyed fellows who helped Vulcan to forge the thunderbolts, must have been clumsy workmen, in spite of what the ancient writers say to the contrary.

Before we consider the use of two eyes, let us examine the structure of a single organ. The eye has often been compared with the camera obscura, that dark box in which an image is formed of external objects, by means of an arrangement of glass lenses. The eye is, indeed, a dark chamber furnished with lenses, but here the likeness ceases, as its marvellous arrangements are infinitely more beautiful than those of any optical instrument devised by the ingenuity of man.