_Analytical_, relating to analysis. _Investigation_, act of searching, or tracing out. _Subordinate_, inferior in nature, dignity or power. Relate a few more of the advantages obtained by a knowledge of Chemistry. Many of the wonderful operations of Nature, and the changes which take place in substances around us, are, by its means, revealed to us. In every manufacture, art, or walk of life, the chemist possesses an advantage over his unskilled neighbor. It is necessary to the farmer and gardener, as it explains the growth of plants, the use of manures, and their proper application: and indispensable to the physician, that he may understand the animal economy, and the _effects_ which certain _causes_ chemically produce; and the nature of animal, vegetable, and mineral poisons. The study is, therefore, an invaluable branch in the education of youth: it is useful, not only in the active, but the _moral_ life, by laying the foundation of an ardent and inquiring mind. Even an everyday walk in the fields can be productive of instruction, by a knowledge of it;--and let us always remember, that "Knowledge is Power." _Indispensable_, necessary, not to be done without. CHAPTER XIX. ATTRACTION, TIDES, GRAVITY, ARTESIAN WELLS, AIR, ANEROID BAROMETER, EAR-TRUMPET, STETHOSCOPE, AUDIPHONE, TELEPHONE, PHONOGRAPH, MICROPHONE, MEGAPHONE, TASIMETER, BATHOMETER, ANEMOMETER, CHRONOMETER. What is Attraction? By attraction is meant that property or quality in the particles of bodies which makes them tend toward each other. Are there several kinds of attraction? Yes. Attraction has received different names, according to the circumstances under which it acts: The force which keeps the particles of matter together to form bodies or masses, is called attraction of _cohesion_; that which makes bodies stick together only on their surfaces, is called _adhesion_; that which inclines different masses toward each other, as the earth and the heavenly bodies, is called _gravitation_; that which forces the particles of substances of different kinds to unite, is known under the name of _chemical attraction_; that which causes the needle of the compass to point constantly toward the poles of the earth, is _magnetic attraction_; that which is excited by friction in certain substances, is known as _electrical attraction_. How do you know that attraction exists through the whole universe? This great universal law was first discovered by Sir Isaac Newton. The sun and planets and other heavenly bodies are only guided in their path by gravitation. Do we experience this attraction upon our earth? Yes; because our earth is carried around the sun by it; and, further, the tides show it very clearly. What are the Tides? The ebbing and flowing of the sea, which regularly takes place twice in twenty-four hours. The cause of the tides is the attraction of the sun, but chiefly of the moon, acting on the waters of the ocean. What is Gravity?