I. Mountains help to condense water-vapour from the atmosphere, thus bringing back to the earth moisture which it loses continually by evaporation. II. Mountains are elevated reservoirs of water in one form or another, and thus not only feed the streams and rivers, but give them force and direction as well. III. Mountains suffer themselves to be slowly worn away in order that the face of the earth may be renewed; in other words, they die that we, and all created things, may live. I. _Mountains help to condense water-vapour from the atmosphere, thus bringing back to the earth the moisture which it loses continually by evaporation._ Every one knows that there is abundance of water-vapour in the atmosphere, but the question arises, How does it get there? The answer to this lies in the simple fact that every surface of water exposed to the air undergoes loss by evaporation. If you wish to satisfy yourself on this point, place a saucer of water in your room, and in a few days it will all be gone. We hang clothes out to dry, and so avail ourselves of this curious power that air has of taking up water in the form of vapour. Steam, or water-vapour, is really invisible, though we frequently talk of seeing the steam issuing from a locomotive; but what we really see is a cloud of condensed steam, and such clouds,[7] like those that we see floating in the air, are really masses of little tiny particles of water which can reflect or throw back the light which falls upon them, and thus they become visible. Again, a kettle of water, if left too long on the fire will entirely boil away. It is all turned into steam, and the steam is somehow hidden away in the air, though a little of it will be condensed into slight clouds by the colder air outside the kettle. [7] It has lately been proved that clouds can only form in air which contains dust, and that each little suspended particle of water contains a speck of dust or a tiny germ of some sort for its nucleus. But how can water stow itself away in the air without being seen or felt?