only a single lifting of his body, it has to lift its own perhaps a thousand times. The sum of all these little lifts would probably give us a considerable one.
The conclusion we have just reached, that man is relatively forty times stronger than the ant, deserves, then, a closer examination; and it may be that the just interpretation of our facts will cause us to believe that the energetic capacity of muscular fibers is nearly uniform in all animals.
There is another illusion in these matters, which we might call psychological. The agility of some animals surprises us. The monad in a drop of water moves so nimbly that we can hardly follow it; and we naturally make a comparison between the distance which an animal can cover in a certain time and its dimensions. The reasoning of this comparison presents a problem somewhat difficult of solution. It is enough to know that we can not draw from the illusion the consequences which we like to see in it.
If I were to attempt an explanation of this agility, which gives small animals so great facility in escaping their enemies, I should look for it in the small momentum of their mass when in flight, by reason of which only a slight effort is required to enable them to change their direction. Incontestably, we can run much faster than mice; nevertheless, it is not easy to catch a mouse in a closed room. Our own mass is an impediment to our agility. By the time we have made a spring in one direction, the mouse has changed his, and we put our hand, too late, where he was. It is very hard even to lay hold of a bird in a narrow cage.
The part of our question that remains to be treated is no less arduous or obscure than that which we have gone over. I will try to throw what light is possible upon it, but I can not flatter myself that I shall fully succeed. M. Plateau some seventeen years ago measured, with the aid of ingenious harnessings and other devices, the muscular force of insects. He deduced from his experiments that, aside from the power of flight, insects have, as compared with vertebrates, an enormous strength in proportion to their weight; and that in the same group of insects the strength varies, as between different species, inversely as the weight, or, in other words, that the smallest insects are the strongest.
Some of his single results were really surprising. While a horse weighing six hundred kilogrammes can hardly support four hundred kilogrammes, or two thirds of his weight, he found May-bugs, weighing a sixth of a gramme, able to support sixty-six times their own weight, or more than ten grammes. Here, then, was a humble and stupid beetle a hundred times as strong in proportion as the proud and sturdy horse. Another little insect, weighing half a decigramme could move a hundred times its weight. By this standard we men ought to be able to struggle with weights of six thousand kilogrammes