Page:Popular Science Monthly Volume 4.djvu/363

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Traveling rapidly and by night, their sudden irruption into a locality, together with the complete destruction of the field and garden crops, tended to make the ignorant peasantry look upon them as a special visitation from Providence for their sins, and will readily account for the extraordinary notions held regarding them.

Many animals migrate from place to place, or take possession of new territory, when food becomes scarce; but we have only one other instance of a living creature migrating in vast numbers to certain destruction, and that is the locust. When their numbers increase beyond the food-producing powers of their natural habitat, they pour in countless millions into the colder regions beyond, smothering each other in their flight, until the ground is covered with their dead bodies to the depth of several inches, and water-courses are choked up by them, until the air is tainted with the smell of their putrid bodies for miles. None of them ever return whence they came. Their course is always onward, until those that escape death by accident are killed by the first cold weather they encounter. And in this way Nature compels, from time to time, a vast body of these creatures to an act of self-destruction in order that the species may not be annihilated.—Abridged from Temple Bar.



IV. Inertia and Force.

F we look for the speculative background of modern physical theories, we find something like this: Originally there was created, or somehow came to be, an indefinite number of absolutely hard and unchangeable particles of matter. There was also created, or somehow came to be, a number of forces, equally unchangeable—the force of attraction, the force of cohesion, heat, electric and magnetic forces, and boon. The forces began to act and continue to act upon the particles of matter, producing inorganic as well as organic forms. These particles and forces are ultimate facts of experience as well as of thought;