The Metallic elements may be sub-divided into the metals of the alkalies, the metals of the alkaline earths, the metals of the earths, and the other metals sometimes called metals proper. 1st. The metallic bases of the alkalies:--potassium, sodium, lithium, ammonium, cæsium, rubidium. 2d. The metallic bases of the alkaline earths:--calcium, strontium, barium. 3d. The metallic bases of the earths:--aluminum, glucinum, zirconium, thorium, yttrium, erbium, cerium, lanthanum, didymium. 4th. The metals proper, the most important of which are:--platinum, gold, silver, mercury, copper, iron, tin, lead, nickel, zinc, bismuth, antimony, manganese, cobalt, arsenic. Now, from these elementary bodies, united together in various proportions, is formed the infinite variety of substances around us, whether animal, vegetable, or mineral; in fact, a few only are generally employed:--in the case of animals and vegetables, oxygen, hydrogen, carbon, nitrogen, with occasionally some sulphur, calcium, phosphorus, and silicon, suffice for building up the beautiful forms of animated nature; while the fabric of our globe itself consists for the most part of the earths; silex, _i.e._, flint or crystal; lime, in the shape of chalk, marble, or limestone, such as our flagstones are composed of; slate and granite, which are compounds of aluminium, silica, and small quantities of oxide of iron, and sometimes a little potash, etc.; and through their masses are projected irregular streams--veins as they are termed--of the metals, either in a pure state, as is the case sometimes with gold, silver, platinum, mercury, and perhaps one or two others; or combined with one of the non-metallic elements, or with one another. Late calculations have determined the composition of the earth’s solid crust in 100 parts by weight to be: Oxygen 44.0 to 48.7. Silicon 22.8 “ 36.2. Aluminium 9.9 “ 6.1. Iron 9.9 “ 2.4. Calcium 6.6 “ 0.9. Magnesium 2.7 “ 0.1. Sodium 2.4 “ 2.5. Potassium 1.7 “ 3.1. ------ ------ 100.0 100.0 ------ ------ All these combinations are effected by certain powers, termed _forces_; those which cause the union of the elements are called the forces of attraction; those causing their separation, the forces of repulsion. The force of attraction when exerted between masses of matter, is termed gravitation; when it unites particles of matter of a similar kind and produces masses, it is called the attraction of cohesion; when the particles united are of a dissimilar character, it is then termed chemical or elective affinity. For example, the crystals of Epsom salts are formed from minute particles of the salt, united into a larger or smaller mass by the attraction of cohesion, while the _elements_ of which each particle consists, namely, the sulphur, oxygen, and magnesium, are united by the attraction of chemical affinity.