ment of ascent in which those individuals are engaged—yields in its every detail an illustration of the mode of all movement. At first, tools were of the rudest kind, and men reached their ends with labor enormous compared with that needed for the attainment of the same ends to-day; but in proportion as they acquired knowledge of the external world, of the properties of things, of how things act and may be acted upon, and of the means and methods by which desired results may be brought about—in proportion, moreover, as human need, widening and becoming more varied with human ascent, made demand for a larger number and a greater variety of implements—in such proportion did men perfect, not only their tools, but also the ends possible of attainment therewith. To the implements, moreover, once used only by individuals, there have been added the tools called into service as social appliances by groups of men, and finally by the whole community. Thus the progress of tools has been an ascent, not only from the sandals of rawhide to the shoe of civilized races, from the knife of stone to the modern blade of steel, from the sticks rubbed together to the lucifer match, from the sling to the rifle, from the bone needle to the sewing machine, and from the gnomon and the clepsydra to the timepiece—it has also meant the gradual development of such social mechanisms as steamboats, railways, street cars, post offices, telegraphs, and the like. Finally, all such improvement, whether of the individual or the social appliance, has been, from first to last, progress in the economy of the labor needed for particular ends and perfection of the ends themselves.
Illustrations of the law of least resistance may also be drawn from the realm of mind. The need of economizing energy in thought is one which, however conscious or unconscious we may be of it, dominates and directs, so to speak, all our mental activities. This is suggested by the familiar antithesis between breadth and profundity of acquirements—by the fact that artistic genius is usually divorced from depth of intellect, that speculative ability is rarely associated with knowledge of the world, that the thinker who is deeply versed in general principles is almost never a specialist, that the poet is only phenomenally a man of affairs, and that the power to think originally and philosophically and the power to excel in the graces of literary style are rarely allied in one and the same individual, or present in any individual at one and the same moment. In a general way, we can concentrate the mind, so to speak, upon any particular object only by abstracting it from all other objects; our attention to a speaker, or a book, ebbs and flows according to the interest we take in particular passages; more than half the familiar activities of our daily life are performed without any attention to them which can properly be called conscious. We are constantly, on the one hand, reserving
