torrid zone, each species being confined to the district best ́ fitted to its existence. Shell-fish decrease in size and beauty with their distance from the equator; and as far as is known, each sea has its own kind, and every basin of the ocean is inhabited by its peculiar tribe of fish. Indeed, MM. Peron and Le Sueur assert, that among the many thousands of marine animals which they had examined, there is not a single animal of the southern regions which is not distinguishable by essential characters from the analogous species in the northern seas. Reptiles are not exempt from the general law. The Saurian tribes of the four quarters of the globe differ in species, and although warm countries abound in venomous snakes, they are specifically different, and decrease both in the numbers and in the virulence of their poison with decrease of temperature. The dispersion of insects necessarily follows that of the vegetables which supply them with food, and in general it is observed, that each kind of plant is peopled by its peculiar inhabitants. Each species of bird has its

peculiar haunt, notwithstanding the locomotive powers of the winged tribes. The emu is confined to Australia, the condor never leaves the Andes, nor the great eagle the Alps; and although some birds are common to every country, they are few in number. Quadrupeds are dis

tributed in the same manner wherever man has not interfered. Such as are indigenous in one continent are not the same with their congeners in another and with the exception of some kinds of bats, no warm-blooded anìmal is indigenous in the Polynesian Archipelago, nor in any of the islands on the borders of the central part of the Pacific.

In reviewing the infinite variety of organised beings.

that people the surface of the globe, nothing is more remarkable than the distinctions which characterise the different tribes of mankind, from the ebony skin of the torrid zone to the fair and ruddy complexion of Scandinavia, a difference which existed in the earliest recorded times, since the African is represented in the sacred writings to have been as black in the first ages of mankind as he is at the present day, and the most ancient Egyptian paintings confirm that truth; yet it appears from a comparison of the principal circumstances relating to the ani mal economy or physical character of the various tribes of mankind, that the different races are identical in species. Many attempts have been made to trace the various tribes back to a common origin, by collating the numerous languages which are, or have been, spoken. Some classes of these have few or no words in common, yet exhibit a remarkable analogy in the laws of their grammatical construction. The languages spoken by the native American nations afford examples of these; indeed the refinement in the grammatical construction of the tongues of the American savages lead to the belief that they must originally have been spoken by a much more civilized class of mankind. Some tongues have little or no resemblance in structure, though they correspond extensively in their vocabularies, as in the Syrian dialects. In all of these cases it may be inferred, that the nations speaking the languages in question are descended from the same stock; but the probability of a common origin is much greater in the IndoEuropean nations, whose languages, such as the Sanscrit, Greek, Latin, German, &c. have an affinity both in structure and correspondence of vocables. In many tongues not the smallest resemblance can be traced; length of

time, however, may have obliterated the original identity.The conclusion drawn from the whole investigation is, that although the distribution of organized beings does not follow the direction of the isothermal lines, temperature has a very great influence on their physical development. Possibly, too, the nature of animated and inanimated creatures may be powerfully modified by the invisible agencies of electricity and magnetism, which probably pervade all the particles of matter; indeed the temperature of the air seems to be intimately connected with its electrical condition.

SECTION XXVIII.

Electricity is one of these imponderable agents pervad ing the earth and all substances, without affecting their volume or temperature, or even giving any visible sign of its existence when in a latent state, but when elicited, developing forces capable of producing the most sudden, violent, and destructive effects in some cases, while in others their action, though less energetic, is of indefinite and uninterrupted continuance. These modifications of the electric force, incidentally, depending upon the manner in which it is excited, present phenomena of great diversity, but yet so connected as to justify the conclusion that they originate in a common principle.

Electricity may be called into activity by mechanical power, by chemical action, by heat, and magnetic influence; but we are totally ignorant why it is roused from its neutral state by such means, or of the manner of its existence in bodies; whether it be a material agent, or merely a

property of matter. However, as some hypothesis is necessary for explaining the phenomena observed, it is assumed to be a highly-elastic fluid, capable of moving with various degrees of facility through the pores or even the substance of matter; and as experience shows that bodies in one electric state attract, and in another repel each other, the hypothesis of two kinds, called positive and negative electricity, is adopted, but whether there really be two different fluids, or that the mutual attraction and repulsion of bodies arises from the redundancy and defect of their electricities, is of no consequence, since all the phenomena can be explained on either hypothesis. As each electricity has its peculiar properties, the science may be divided into branches, of which the following notice is intended to convey some idea.

Substances in which the positive and negative electricities are combined, being in a neutral state, neither attract nor repel; but there is a numerous class called electrics, in which the electric equilibrium is destroyed by friction; then the positive and negative electricities are called into action or separated; the positive is impelled in one direction, and the negative in another; those of the same kind repel, whereas those of different kinds attract each other. The attractive power is exactly equal to the repulsive force at equal distances, and when not opposed, they coalesce with great rapidity and violence, producing the electric flash, explosion, and shock; then equilibrium is restored, and the electricity remains latent till again called forth by a new exciting cause. One kind of electricity cannot be evolyed without the evolution of an equal quantity of the opposite kind: thus, when a glass rod is rubbed with a piece of silk, as much positive electricity is elicited

in the glass as there is negative in the silk. The kind of electricity depends more upon the mechanical condition than on the nature of the surface, for when two plates of glass, one polished and the other rough, are rubbed against each other, the polished surface acquires positive, and the rough negative electricity. The manner in which the friction is performed also alters the kind of electricity. Equal lengths of black and white ribbon, applied longitudinally to one another, and drawn between the finger and thumb, so as to rub their surfaces together, become electric; when separated, the black ribbon is found to have acquired negative electricity, and the white positive: but if the whole length of the black ribbon be drawn across the breadth of the white, the black will be positively, and the white negatively electric when separate. Electricity may be transferred from one body to another in the same manner as heat is communicated, and, like it too, the body loses by the transmission. Although no substance is altogether impervious to the electric fluid, nor is there any that does not oppose some resistance to its passage, yet it moves with much more facility through a certain class of substances called conductors, such as metals, water, the human body, &c., than through atmospheric air, glass, silk, &c., which are therefore called non-conductors; but the conducting power is affected both by temperature and moisture.

Bodies surrounded with non-conductors are said to be insulated, because, when charged, the electricity cannot escape; but when that is not the case, the electricity is conveyed to the earth, which is formed of conducting matter; consequently it is impossible to accumulate electricity in a conducting substance that is not insulated. There