But may we not ascend, in our reasoning, from animal life to human thought and character, and find the same law operative? As human health, form and vigor are found to vary with phenomena of climate, such as heat and cold, moisture and dryness, and with geographical location among mountains and valleys, or on broad plains, by the sea-coast or in the interior, so do we not notice that mental and moral development depend upon the outward circumstances amid which one lives? Our natures are plastic, and easily take the impress of objects with which we come continually in contact. Education is not merely that from books, but that also which is received from all manner of surrounding influences, as they exist in the home, in social intercourse and in the community at large. We see whole nations continue, century after century, on the same low level of barbarism, because no change occurs in their outward circumstances to bring new forces to act upon them. Our Indian tribes are an illustration. They live, out on the western plains, precisely as their fathers did for ages before them; and thus they will live so long as the modifying influence of civilization does not reach them, and bring a change of environment. Let such a change occur, however, and a revolution takes place, whatever race may be involved. Even the most favored nations improve rapidly, when any external fact comes in, to change circumstances, and thus to alter the current of thought and the channel of action. Think how much of modern civilization is owing to three things, themselves external and mechanical, yet powerfully affecting mind by their incidental effects—the invention of gunpowder, of the mariner’s compass and of printing. But if, in addition to new inventions and industries, there be brought in schools and churches, to operate directly on mind and heart, the effect is like placing people in a new climate. It is, indeed, scarcely a figure of speech, when we sometimes speak of an intellectual and moral atmosphere—meaning thereby the totality of constant influences in a community, which affect opinion, modify character and control conduct. As we breathe the air, every moment of every day, thinking little of the fact, yet continually drawing in health or sickness, life or death, so are we unconsciously but most really influenced for good or evil by all that is going on around us; by public opinion, social customs, example of friends and neighbors, existing institutions, industries, amusements, studies, reading, conversation and religious exercises.