of memory, have as a basis the association of ideas. It may be admitted at once that many high processes of thought involve the following of association along many lines at once, or in such a complex way that to picture them clearly to the mind would be an almost impossible task. But there appears to be no essential difference in kind between the simple conclusions which have been used as illustrations and the more complex ones involved in abstract reasoning. The logician will reduce all your acts of reasoning to certain syllogisms which it is now quite customary to express in algebraic formulæ. For each of these formulæ it is possible to picture a physical basis of nerve-cells, joined together by nerve-fibers, so that it seems probable that the mechanism of thought will some day be understood. Our thoughts are usually so rapid and so many that we do not stop to analyze them, but, when we do, we find them always the result of a gradual accretion of ideas and not a new creation. The inventor will tell you that his most brilliant discovery did not spring suddenly into his mind in all its perfection, but was gradually led up to, step by step, with many halts and puzzling alternatives. Finally, old mechanisms and principles, formerly familiar, were successfully associated together with new adaptations into a new unit, and the ingenious mechanism was complete. The evolution of the locomotive, of the telegraph, and of the telephone teaches us the process in the inventor's mind as clearly as it shows his genius for construction. There are many other mental processes which might be followed out which display equally well how closely reasoning depends on the association of ideas—i.e., upon the play of consciousness along lines of communication between different regions of the brain. But we must pass on to some illustrations of action.
Watch a game of tennis and notice the difference between players, and you can tell a great deal about their mental processes. One is quick to see the ball, to note its direction, and to calculate its speed and the position it will reach in a moment, and yet from a lack of quickness in movement or from clumsiness he is unable to return it well. Another is particularly agile and graceful, plays all over the field, and seems to be everywhere at the right time; and you think him the better player. But as you watch you find that he judges the ball badly, and is not accurate in his calculation as to where it is going or when it will fall. The champion player is the one who combines accuracy and quickness with precision and agility. The sight of the direction of the ball leads him at once to a correct judgment of how far he has to run or reach for it, and his movement is quick enough and directed with just sufficient force to make the return. Now, this matter of precision of movement is dependent upon a process of perception,