Page:The fairy tales of science.djvu/59

Rh We must remember that this aërial ocean is some forty-five miles in depth, and that the vapours which arise from the earth are rapidly diffused throughout its entire extent.

The atmosphere exerts a pressure upon the earth's surface equal to about fourteen and a half pounds upon each square inch; and it has been calculated that its entire weight amounts to more than five thousand one hundred and fourteen billions of tons—a sum which words may express, but which the human mind cannot appreciate. Our readers will gain a clearer conception of this enormous sum when we tell them that it is equivalent to the weight of a solid globe of lead some sixty miles in diameter!

We have said that the atmosphere contains an aëriform body called carbonic acid. Let us now see how this fact may be proved. When quicklime is exposed to the air it gradually loses its caustic properties, and increases in weight; this increase of weight depends on the absorption of carbonic acid from the surrounding atmosphere.

We may expel this gas from the altered lime by heat, and collect it in suitable vessels for examination. We find it to be much heavier than ordinary air—so heavy, indeed, that we may pour it from one vessel to another, like water. If we plunge a lighted taper in it the flame will be instantly extinguished; and if we substitute a mouse or any other small animal for the taper, the poor creature will be suffocated.