[AS.] The fluid which falls in rain ana forms rivers and seas. Like air, water was formerly considered a simple substance; but about a century ago the compound nature of water was discovered. Now it is a familiar fact that it is composed of two elements, oxygen and hydrogen, in the proportion of two parts of hydrogen to one of oxygen. At temperatures below freezing point (32° F.) water exists in the solid form of ice ; between freezing point and boiling-point (2120 F.) it takes the liquid form; and above boiling-point it exists in a gaseous state as vapor or steam. When the sun shines on the seas and rivers, the heat evaporates daily a quantity of water. Rising up into the air, and carried along by the winds, this water-vapor is condensed, and fells as rain. Rain-water is in reality a kind of distilled water. It is not perfectly pure, for in falling it dissolves some of the carbonic acid gas out of the air, and also brings down impurities as soot. Water containing carbonic acid dissolves limestone and gains a condition called hardness, which may be removed by boiling or by adding lime-water. Pure water is clear, without taste, and colorless. Water is most commonly seen in the liquid state, but it is easily converted into a solid or into a gas. When liquid water is cooled, it contracts, or becomes less in size, until it reaches 300 ; if cooled still more, it begins slowly to expand; but when it is as cold as 32°, it suddenly expands, becoming about one-tenth larger, and forming the solid called ice. This is the reason why water-pipes often burst in frosty weather. The blood, which carries the food to all parts of the body, and removes the waste matter from every organ, is more than three parts water ; more exactly, in 100 lbs. of blood there are 79 lbs. of water. Water forms about two-thirds of the total weight of the body. In 100 lbs., lettuce contains 96 lbs.; cabbage, 92; apples, 83; fish, 78; potatoes, 75 ; lean meat, 72 ; bread, 40; cheese, 34; rice, 15 ; butter, 10, parts of water.

A DROP OF WATER, MAGNIFIED.

A DROP OF WATER, MAGNIFIED.