tions, 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 those imponderable agents pervading 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 modifica tions 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 by 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 evolved 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 per formed 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 are a great many substances called non-electrics, in which electricity is not sensibly developed by friction, unless they be insulated, probably because it is carried off by their conducting power as soon as elicited. Metals, for example, which are said to be non-electrics, can be excited, but, being conductors, they cannot retain this state if in communication with the earth. It is probable that no bodies exist which are either perfect nonelectrics or perfect non-conductors; but it is eviIdent that electrics must be non-conductors to a certain degree, otherwise they could not retain their electric state. It has been supposed that an insulated body remains at rest, because the tension of the electricity, or its pressure on the air which restrains it, is equal on all sides; but when a body in a similar state, and charged with the same kind of electricity, approaches it, that the mutual repulsion of the particles of the electric fluid diminishes the pressure of the fluid on the air on the adjacent sides of the two bodies, and increases it on their remote ends; consequently that equilibrium will be destroyed, and the bodies, yielding to the action of the preponderating force, will recede from or repel each other. When, on the contrary, they U |