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exercise in observation; and this is as far as the juvenile capacity can go. It is neither fitting nor possible that tremendous ideas should make a profound impression upon a child's mind. It has no capability either to appreciate or to receive them. Savages are incapable of wonder; they do not know enough to wonder. Said Professor Grove, in his address before the British Association at Nottingham, "If the primitive inhabitants of Britain could emerge and behold the wonderful triumphs of art and science in our civilization, it is doubtful if they would know enough to be astonished." And so with children. We may teach them to say of the stars, "How I wonder what you are!" but they do not wonder in the least. Only minds highly cultivated and widely informed are capable of appreciating the tremendous idea of evolution so as to be deeply impressed by it. We are not to suppose, because the young readily acquire terms and phrases, and seem in a way to understand them, that they are therefore in possession of their real and full meanings. There are stages in the process of assimilating ideas which the pupil reaches one after another in the slow course of mental unfolding. Before the period of its formal education, in the natural development of mind, the child never leaps forward into the complex and difficult, but insensibly grows into greater and greater strength through its spontaneous interest in simple things. This is the safest course to follow, because we are here on the solid ground of Nature's own method.



IF it were usual to prefix a motto to these evening discourses, I might have selected such words as "Seeing the Invisible," for I have to describe a method of investigation by which what is usually unseeable may become revealed. We live at the bottom of a deep ocean of air, and therefore every object outside the earth can be seen by us only as it looks when viewed through this great depth of air. Professor Langley has shown recently that the air mars, colors, distorts, and therefore misleads and cheats us to an extent much greater than was supposed. Langley considers that the light and heat absorbed and scattered by the air and the particles of matter floating in it amount to no less than forty per cent of the light falling upon it. In consequence of this want of transparency and of the presence of finely divided matter always more or less suspended in it, the air, when the sun shines upon it, becomes itself a source of light. This illuminated

  1. A lecture delivered at the Royal Institution of Great Britain, Friday evening, February 20, 1885.