33 POPULAR SCIENCE MONTHLY. 



ment of ascent in whicli 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 attain- 

 ment 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 pro- 

 portion, 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 per- 

 fect, not only their tools, but also the ends possible of attainment 

 therewith. To the implements, moreover, once used only by in- 

 dividuals, there have been added the tools called into service as 

 social appliances by groups of men, and finally by the whole com- 

 munity. 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 o\ 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 activi- 

 ties. 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 spe- 

 cialist, 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 pas- 

 sages ; 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 



