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water. These constitute the source of the river, and are usually found among hills.

2. Thus the Severn has its source in the Welsh Mountains; the Thames in the Cotswold Hills; the Danube in the hills of the Black Forest; the Rhine and the Rhone in the Alps.

3. But it is quite plain that we have not yet reached the real beginning of

the rivers. Whence do the earliest streams derive their water? A brief residence among the mountains would prove to you that they are fed by rains. In dry weather you would find the streams feeble, sometimes indeed quite dried up. In wet weather you would see them foaming torrents.

In general, these streams lose themselves as little threads of water upon the hill-sides; but sometimes you may trace a river to a definite spring. The river Albula in Switzerland, for instance, rushes at its origin in considerable volume from a mountain side. But you very soon assure yourself that such springs are also fed by rain, which has percolated through the rocks or soil, and which, through some orifice that it has found or formed, comes to the light of day.

4. But we cannot end here. Whence comes the rain which forms the mountain streams? Observa

[graphic]

tion enables you to answer the question. Rain does not come from a clear sky. It comes from clouds. But what are clouds? Is there nothing you are acquainted with which they resemble? You discover at once a likeness between them and the condensed steam of a locomotive. At every puff of the engine a cloud is projected into the air. Watch the cloud sharply: you notice that it first forms at a little distance from the top of the funnel. Give close attention and you will sometimes see a perfectly clear space between the funnel and the cloud. Through that clear space the thing which makes the cloud must pass. What, then, is this thing which at one moment is transparent and invisible, and at the next moment visible as a dense opaque cloud?

5. It is the steam or vapour of water from the boiler. Within the boiler this steam is transparent and invisible; but to keep it in this invisible state, a heat would be required as great as that within the boiler. When the vapour mingles with the cold air above the hot funnel it ceases to be vapour, and becomes a minute particle of water. The liquid particles thus produced form a kind of water-dust of exceeding fineness, which floats in the air, and is called a cloud.

6. Watch the cloud-banner from the funnel of a running locomotive; you see it growing gradually less dense. It finally melts away altogether, and if you continue your observations you will not fail to notice that the speed of its disappearance depends upon the character of the day. In humid weather the cloud hangs long and lazily in the air; in dry

weather it is rapidly licked up. What has become of it? It has been reconverted into true invisible.

vapour.

7. The drier the air, and the hotter the air, the greater is the amount of cloud which can be thus dissolved in it. When the cloud first forms, its quantity is far greater than the air is able to maintain in an invisible state. But as the cloud mixes gradually with a larger mass of air it is more and more dissolved, and finally passes altogether from the condition of a finely-divided liquid into that of transparent vapour or gas.

8. Make the lid of a kettle air-tight, and permit the steam to issue from the pipe; a cloud is precipitated in all respects similar to that issuing from the funnel of the locomotive.

9. Permit the steam as it issues from the pipe to pass through the flame of a spirit-lamp, the cloud is instantly dissolved by the heat, and is not again precipitated. With a special boiler and a special nozzle the experiment may be made more striking, but not more instructive, than with the kettle.

[blocks in formation]

per-col-at-ed, filtered or flowed re-con-vert'-ed, turned again.

through.

or'-i-fice, opening or mouth.

lo-co-mo'-tive, railway engine. pro-ject'-ed, sent out.

dis-solved', melted down.

pre-cip'-i-tat-ed, thrown out in a

denser or more visible form.

noz-zle, nose or point.

EXERCISES.-1. Make verbs from the following verbs: Divide (subdivide), trace, appear, solve, operate, navigate (circumnavigate).

2. Make verbs from the following verbs by changing the prefix : Commit, revert, proceed, export, occur, suppress, subject, suffer,

consist.

3. Make nouns from the following nouns: River (rivulet), stream, forest, engine, steam, lance.

4. Make sentences of your own, and use in each sentence one or more of the following words: Invisible, derive, dissolve, constitute.

THE

ORIGIN OF RIVERS-II.

1. Look to your bedroom windows when the weather is very cold outside; they sometimes stream with water derived from the condensation of the aqueous vapour from your own lungs. The windows of railway carriages in winter show this condensation in a striking manner. Pour cold water into a dry drinking-glass on a summer's day: the outside surface of the glass becomes instantly dimmed by the precipitation of moisture. On a warm day you notice no vapour in front of your mouth, but on a cold day you form there a little cloud derived from the condensation of the aqueous vapour from the lungs.

2. You may notice in a ballroom that as long as the door and windows are kept closed, and the room remains hot, the air remains clear; but when the doors or windows are opened a dimness is visible, caused by the precipitation to fog of the aqueous vapour of the ballroom. If the weather be intensely cold, the entrance of fresh air may even cause snow to fall. This has been observed in Russian ballrooms; and also in the subterranean stables at

Erzeroum, when the doors are opened and the cold morning air is permitted to enter.

3. Even on the driest day this vapour is never absent from our atmosphere. The vapour diffused through the air of a room may be congealed to hoar frost in your presence. This is done by filling a vessel with a mixture of pounded ice and salt, which is colder than the ice itself, and which, therefore, condenses and freezes the aqueous vapour. The surface of the vessel is finally coated with a frozen fur, so thick that it may be scraped away and formed into a snowball.

4. To produce the cloud in the case of the locomotive and the kettle, heat is necessary. By heating the water we first convert it into steam, and then by chilling the steam we convert it into cloud. Is there any fire in nature which produces the clouds of our atmosphere? There is: the fire of the sun.

5. Thus, by tracing backward, without any break in the chain of occurrences, our river from its end to its real beginnings, we come at length to the

sun.

6. There are, however, rivers which have sources somewhat different from those already mentioned. They do not begin by driblets on a hill-side, nor can they be traced to a spring. Go, for example, to the mouth of the river Rhone, and trace it backwards to Lyons, where it turns to the east. Bending round by Chambery, you come at length to the Lake of Geneva, from which the river rushes, and which you might be disposed to regard as the source of the Rhone. But go to the head of the lake, and you find that

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