Arbor Day Manual. Charles Skinner. Bardeen & Co. $2.50. Songs of Nature. John Burroughs. McClure, Phillips & Co. $1.50. Among Flowers and Trees. Wait & Leonard. Lee & Shepherd. $2.00. LEAFLET VI. A SUMMER SHOWER.[8] BY R. S. TARR. [8] Teachers' Leaflet, No. 14: Cornell Nature-Study Bulletin, June, 1899. [Illustration] A Rainstorm comes, the walks are wet, the roads are muddy. Then the sun breaks through the clouds and soon the walks are no longer damp and the mud of the road is dried. Where did the water come from and where has it gone? Let us answer these questions. A kettle on the stove is forgotten and soon a cracking is heard; the housewife jumps to her feet for the kettle is dry. The kettle was filled with water, but it has all boiled away; and where has it gone? Surely into the air of the room, for it can be seen issuing as "steam" and then disappearing from view, as if by magic. The heat of the fire has changed the liquid water to a gas as invisible as the air itself. This gas is _water vapor_. [Illustration: _Fig. 9. A glass of cold water on which vapor has condensed in drops._] Do you wish to prove that the water vapor is there, although unseen? Then, if the day is cool, watch the window and notice the drops of water collect upon it. Or, if the day is warm, bring an ice-cold glass or pitcher into the room and see the drops collect upon it (Fig. 9). People sometimes say, when drops of water collect on a glass of cold water, that the glass is "sweating;" but see whether the same thing will not happen with a cold glass that does not contain water. These two simple observations teach us two very important facts: (1) That heat will change liquid water to an invisible vapor, or gas, which will float about in the air of a room; and (2) that cold will cause some of the vapor to change back to liquid water. Let us observe a little further. The clothes upon the line on wash day are hung out wet and brought in dry. If the sun is shining they probably dry quickly; but will they not dry even if the sun is not shining? They will, indeed; so here is another fact to add to our other two, namely (3) that the production of vapor from water will proceed even when the water is not heated. This change of water to vapor is called _evaporation_. The water evaporates from the clothes; it also evaporates from the walks after a rain, from the mud of the road, from the brooks, creeks and rivers, and from ponds, lakes, and the great ocean itself. Indeed, wherever water is exposed to the air some evaporation is taking place. Yet heat aids evaporation, as you can prove by taking three dishes of the same kind and pouring the same amount of water into each, then placing one on the stove, a second in the sun, and a third in a cool, shady place, as a cellar, and watching to see which is the last to become dry.