should have perceived that the apparent calm had no real existence. On the contrary, it would have directly appeared that the ultimate molecules of the air were in a condition of exuberant liveliness.
No doubt the smallest particle of air which could be directly appreciable by any of our appliances for measurement, seems a homogeneous structure and perfectly quiescent in its several parts. When, however, we conduct the examination into its character by those refined methods of investigation which are now at our disposal, we find that the air is ultimately composed of myriads of separate particles. Each of these little particles, no matter how quiet the air as a whole may seem, is in a state of intensely rapid movement. Picture to yourself incalculable myriads of little objects, each dashing about with a speed as great as that of a rifle bullet, and often indeed far greater. The little particles are so minute that it would take about fifty millions of them, placed side by side, to extend over a single inch. The smallest object which we can discern with a microscope is perhaps one hundred-thousandth of an inch in length. The little gaseous molecule would therefore require to possess a diameter about five hundred times greater than that which it actually has, if it were to be large enough to admit of inspection by the utmost microscopic powers which we could bring to bear upon it. And yet, notwithstanding the fact that these particles are so extremely minute, we are able to reason about their existence, to discover many of their properties, and to ascertain the laws of their action in such a way as to throw light into many obscure places of nature. I do not, indeed, know any doctrine in modern science of a more instruc-
