These wonderful hot springs, wherever they have been found, have excited the greatest attention and interest, in travellers and scientific men, and their workings have been explained somewhat in this way:—
Water having gradually accumulated in vast underground crevices and cavities, is heated by the fires, which, in volcanic regions, are not very far from the surface of the earth. If there is a channel or tube from the reservoir to the surface, the water will expand and rise until it fills the basin which is generally found at the mouth of hot springs. But the water beneath, being still further heated, will be changed into steam, which will at times burst out with great force, carrying with it a column of water high into the air. When this water falls back into the basin it is much cooler, on account of its contact with the air, and it cools the water in the basin, and also condenses the steam in the tube or channel leading from the reservoir. The spring is then quiet until enough steam is again formed to cause another eruption. A celebrated German chemist named Bunsen constructed an apparatus for the purpose of showing the operations of Geysers. Here it is.
You see that the two fires in the engraving—one lower and larger than the other, because the heat of the earth increases as we get farther from the surface—will heat the water in the iron tube very much as water is heated in a real Geyser; and when steam enough is formed, a column of hot water is thrown out of the basin. The great subterranean reservoir is not imitated in this apparatus, but the action is the same as if the tube arose from an iron vessel. There is a great deal in Bunsen's description of this contrivance, in regard to the difference in the temperature of the water in that part of the tube between the two fires, and that in the upper portion, which explains the intermittent character of the eruptions of a Geyser, but it is not necessary for us to go into all his details.
When we know that under a Geyser the water is boiling in a great reservoir which communicates with the surface by a natural tube or spout, we need not wonder that occasionally a volume of steam bursts forth, sending a column of water far into the air.
A GIANT PUFF-BALL.
I suppose you have all seen puff-balls, which grow in the fields like mushrooms and toadstools, but I am quite sure that you never saw anything of the kind quite so large as that one in the picture. And yet that engraving was made from a drawing from the puff-ball itself. So we need not suppose that there is anything fanciful about it.