the same absolute height, each one performs a work precisely proportional to its mass; and, when a man leaps over an obstacle sixty centimetres from the ground, he accomplishes, other conditions being the same, a task as considerable again as that of the flea or the grasshopper, which can not spring much above thirty centimetres.
A few figures will make the matter plain. Take a grasshopper weighing six decigrammes (nine grains), and a man weighing sixty kilogrammes (one hundred and fifty pounds). The man is equivalent in weight to a hundred thousand grasshoppers. But a hundred thousand grasshoppers grouped into a single mass could only raise that mass thirty centimetres, while the man can lift his own mass sixty centimetres. All the advantage, then, is on the side of the man. Here is a wide variance from the strength which has been exacted of the horse to make him a rival of the flea.
The basis of the comparison was vicious. The height or volume of the agent who handles a weight has nothing to do with the estimation of the labor. A sack of meal is no heavier on the shoulders of a man than on the loins of a horse. The labor and the effort have been confounded. The labor is a defined and absolute quantity; the effort a vague and variable sensation.
The deductions respecting speed have no better foundation. The ant, as a moving body, is a little mass of matter on which a determined force impresses a speed of two and a half metres a minute. To impress the same speed on a mass of fifteen millions of ants—which I take to represent the volume of a man—would require a force fifteen millions greater. This force is developed by a man going two and a half metres a minute, while in the same space of time he can easily accomplish a hundred metres and more. In this case, then, if we take notice of any one of the data, the man manifests a strength forty times greater in proportion than that of the ant. This is a very different result from the one arrived at by the other method. Other data, however, com in to complicate the comparison and considerably modify the result.
A little closer study of the phenomena of walking will show us that it absorbs a considerable quantity of force that does not appear in speed. It is not simply a uniform transportation of the body along an horizontal line; but at each step the body is raised, and falls again. The incessant repetition of the lifting is a great cause of fatigue. Hence, walking on an uneven road tires us greatly. In the best paths, the differences of level which have to be overcome correspond with a notable quantity of force lost from speed. The ant, however, being a creeping thing, and supported on six feet, has to raise only a very small part of its weight at each step, and is therefore more advantageously formed than the man, who, having only two feet, gives to his whole body a double oscillation—sidewise, and up and down. On the other hand, the ant feels even the slightest inequalities of the ground. When it goes over the space that represents a man's step, and requires