longer than the height of the flask, to withinabout 1 or 2 cm. of the bottom of the flask. This last tube should be slightly drawn out at the end and bent at the top so that it slants away from the flask. Arrange the flask on a ring stand so that it can be heated by a Bunsenburner. Connect to the tube (a) a rubber tubeFig. 112.
long enough to reach into a water reservoir placed higher than the top of theflask and to one side. Fill the reservoir with water.
Through the tube (b) suck the air out of the flask until the water from the reservoir begins to run into the flask. A siphon will be formed which, when there is no internal pressure, will keep the water in the flask slightly above the bottom of the tube (b). Now heat the flask. When steam begins to form, hot water will be thrown out of the tube (b) until its lower end becomes uncovered and the pressure of the steam relieved. Water from the reservoir will then run in again slightly covering the end of the tube. As soon as more steam is formed, hot water will be ejected as before. Thus a spray of hot water is intermittently ejected from the flask as long as heating continues. We have here an action which resembles that of a geyser.
In the north island of New Zealand, in Yellowstone National Park and in Iceland, remarkable spouting springs called geysers are found. These places have had recent volcanic activity. The eruption of a largegeyser is a most picturesque and startling phenomenon. Almost without warning there is thrown into the air a column of hot water from which the steam escapes in rolling clouds. It rises in some cases to a height of a hundred feet or more and is maintained at nearly this height by the ceaseless outrushing of the water for a time varying from a few minutes to between one and two hours. Then it gradually quiets down and dies away into a bubbling spring of hot water.
The time at which most geysers will erupt is uncertain, but there is one, OldGIANT GEYSER IN ERUPTION.
Faithful, in Yellowstone Park, which is almost as regular as a clock, the time between its eruptions being a little over an hour. This geyser plays to the height of about 150 ft. and maintains the column of water for about four minutes. The Giant Geyser of the same region throws a large column of water to a height of 250 ft. It plays from one to two hours.
The outpouring hot water brings up with it dissolved rock and as the spray falls back and cools, this is deposited, forming craters of singular shape and grotesque beauty. On looking into these craters a smoothlyCONE OF THE BEEHIVE GEYSER.
Built from the dissolved material brought up by the hot water.
lined, irregular, crooked, tubelike opening is seen to extend down into the ground. It is through this that the water finds its way to the surface. How long these tubes are nobody knows, but they must reach to a point where the heat is sufficient to raise water to its boiling point. This heat is probably due to hot sheets of lava.
When the water in the tube is heated enough to make it boil under the pressure to which it is subjected, steam forms and some of the water is pushed out over the surface. This escape of water relieves some of the pressure, and more of the water far down in the tube expands into steam thus throwing more water out. Huge indeed must be the reservoir to which the tube in a geyser like the Giant leads, to be able to pour out such a vast quantity of water.
153.Run-off. -The rain that falls upon the land and neither evapo-rates nor sinks into the surface runs off as fast as it can toward the sea. It is joined sooner or later by the water from the springs and by the rest of the underground drainage. Sometimes the journey is long and there are many stops and delays in lakes and pools; sometimes the course is quite direct and quickly traveled. The run-off most profoundly affects the earth"s surface. Gullies and valleys are cut, depressions are filled; in fact, running water is the chief tool which has carved the features of the earth. It has had a long time to act and it has kept unremittingly busy, so that the results of its action appear now in our varied landscape.
154.Pools and Lakes. -The water which runs off the surface firstfills the depressions. As soon as these are filled, it runs over the lowestpart of their rims and starts again on its course to the greatest of all depressions, the sea. If depressions of considerable size become filled with water, we call them lakes. As with moun- tains, the term lake givesno definite idea as to size. AN UNDRAINED UPLAND.
In some localities a water surface of a few acres is called a lake, while in other localities, the area must be several square miles to merit this name. As a rule, when the area covered by water is small, it is called a pool or a pond.
The streams that flow into lakes are continually bringing down thesand and mud they have gathered in their course, and are thus filling up the lakes. Lake Geneva in Switzerland has had its narrow eastern end filled, for a distance of fifteen or more miles, with the coarseSUNSET ON GREAT SALT LAKE.
sediment brought down by the Rhone. The whole basin of the lake has been covered to an unknown depth by the finer sediment. The outlet to a lake tends to wear away its bed, but it does this slowly, as it has little sediment with which to scour. Thus lakes are being constantly both filled and drained, and so are comparatively short-lived features of the earth. Rivers which have lakes along their courses must be young as otherwise they would have filled or drained the lakes.
Lakes are very important features to man. They filter river water sothat rivers emerging from lakes are clear. Where the Rhone enters LakeTHE DEAD SEA.
