natural state, and again becoming susceptible of being attracted, either by an excited electric, or by another body, to which electricity has previously been communicated. If a rod of glass be applied instead of the finger or metallic rod as above, the body touched remains unaffected, notwithstanding the contact. We are thus led to conclude that some substances, such as glass, are incapable of conducting electricity; while others, such as metals and the human body, readily conduct it. And it is found that all electrics are non-conductors, while, on the contrary, conductors are non-electrics. The permanence of electricity in metallic bodies, suspended in the air by silken thread, proves that the air, as well as silk, is a non-conductor; from which circumstance bodies surrounded by it, except on one side, and this side being in contact with a non-conductor, are said to be insulated. If this condition be not observed, that is, if a body be in contact with conducting substances which communicate with the earth, its electricity will escape through them to the earth, which may be regarded as the great reservoir, both for the absorption and supply of this fluid. The insulating power of the atmosphere depends upon its density and its dryness. In proportion as the air is rarefied by the removal of the superincumbent pressure, its power of confining electricity diminishes, till, at length, when the rarefaction is very great, it opposes scarcely any resistance to the passage of electricity. The presence of moisture in the air also diminishes its insulating power. Water is a good conductor of electricity; accordingly, any portion of it suspended in the air tends to carry off electricity from bodies charged with it, and which are immersed in such an atmosphere. Moisture also easily attaches itself to glass and other electrics, depriving them of the power of insulation. Hence we discover the reason why experiments which succeed in a clear, dry day, will of ten fail in damp weather; and the utility of drying all the instruments employed in electrical experiments, in order to exclude, as much as possible, the interference arising from the presence of condensed moisture. The conducting powers of most bodies are influenced by changes of temperature, and also of form. Thus water, in its liquid state, is a ood conductor; but when in the state of ice, at a temperature of 13° Fahr., it is a non-conductor, and capable of being excited by friction like any other electric. Reducing substances to powder has an effect upon their powers

of conducting electricity. Snow conducts less readily than ice at the same temperature; but glass, as well as sulphur, on the contrary, acquire some conducting power by being pulverized. Vegetable and animal substances lose their conducting powers when made thoroughly dry. No substance with which we are acquainted can be said to be wholly impervious to electricity; nor, on the other hand, is there any body which opposes no resistance to the transmission of electricity. The following table presents a view of the principal classes of bodies, arranged in a series, beginning with those possessed of the greatest conducting power, and terminating with those that have the least. The order in which they possess the power of insulating, is, of course, the reverse of this:

cumstances, are, 1. the imperfection of the insulating property in the solids by which they are supported; 2. the contact of successive portions of air, every particle of which carries off a certain quantity of electricity; 3. the deposition of moisture upon the surface of the insulating bodies, which establishes communications between their opposite ends, and may be considered as virtually increasing their conducting power. Still another circumstance, which materially affects the dissipation of electricity, is the shape of the body in which it is accumulated. The form most favorable for its retention is that of a sphere; next, a cylinder terminated at both extremities by a hemisphere. On the other hand, electricity escapes most readily from bodies of a pointed figure, especially if the point projects to a distance from the surface. In such bodies, it is scarcely possible to retain any accumulation of the electric fluid; whereas, pointed bodies receive electricity more readily than those of any other form.Electric excitation in different bodies exhibits different phenomena. We have seen that light substances excited by glass repel one another, and are likewise repelled by the excited glass. The same thing also happens with respect to bodies which have received their electricity from excited sulphur, or sealing-wax. But on examining the action of any of the bodies of the former class upon any of those belonging to the latter, we find that, instead of repelling, they attract each other; and what is still more remarkable, the instant these bodies come in contact, provided they have both been electrified in an equal degree, they cease at once to exhibit any signs of electrical excitement; the electricity in the one appearing to neutralize that in the other. Thus we seem to have evidence of two kinds of electricity; and as these were first noticed, the one in glass and the other in resinous bodies, they were named vitreous and resinous electricity. Their mode of action on matter has been expressed by the following general law, viz.: Bodies charged with either species of electricity, repel bodies charged with the same species, but attract bodies charged with the other species; and at equal distances, the attractive power in the one case is exactly equal to the repulsive power in the other. Accordingly, we learn the kind of electricity with which a given body is charged, by approaching it to an insulated pith ball, which has previously been touched either with excited glass, or with excited sealing-wax. It is known,

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moreover, that, when two electrics are rubbed against one another, the one acquires, always, one kind of electricity, the other the opposite; and both are produced in equal degrees. Thus, when glass is rubbed by silk or flannel, just as much resinous electricity is produced in the silk or flannel, as there is vitreous electricity produced in the glass; and, consequently, as they are endowed with opposite electricities, there should be an attraction existing between the excited surfaces of the bodies rubbed. This fact is easily proved by the simple and familiar experiment of the ribbons. If a white and a black ribbon, of two or three feet long, and perfectly dry, be applied to each other by their smooth surfaces, and are then drawn repeatedly between the finger and thumb, so as to rub against each other, they will be found to adhere together, and, if pulled asunder at one end, will rush together with great quickness; while united, they exhibit no sign of electricity, because the operation of the one is just the reverse of that of the other, and their power is neutralized and inoperative. If completely separated, however, each will manifest a strong electrical power, the one attracting those bodies which the other repels. The causes that determine the species of electricity excited in the respective bodies, of which the surfaces are made to rub against each other, have not been satisfactorily ascertained. The mechanical configuration of the surfaces appears to have more influence in the result, than the nature of the substances themselves. Thus smooth glass acquires vitreous electricity by friction with almost every substance, except the back of a cat, which induces the resinous electricity; but roughened glass, if rubbed with the same substances, becomes charged with resinous electricity, while the rubbing bodies acquire the vitreous. Silk, rubbed by resin, takes the vitreous, but with polished glass, the resinous electricity. The following is a list of several substances, which acquire vitreous electricity, when rubbed with any of those which follow it, in the order in which they are set down; and resinous electricity, if rubbed with any of those which precede:The back of a cat. Woollen cloth. Polished glass. Feathers. Wood.

Paper.
Silk.
Gum-lac.
Roughened glass.

In the experiment above mentioned of the silk ribbons, the black ribbon exhibited the vitreous, and the white one the res

inous electricity. But when the ribbons are differently excited, as the one being drawn lengthwise and at right angles over a part of the other, the one which has suffered friction in its whole length acquires vitreous, and the other resinous electricity. Indeed, the slightest difference in the conditions of these and similar experiments, or the species of electricity arising from friction, will be often sufficient to produce opposite results. Another important observation, with regard to electrical phenomena, requires to be stated previous to our conclusion of the present head. Whenever a body is charged with electricity, although it be perfectly insulated, it tends to produce an opposite electrical state in all the bodies in its vicinity, and this with greater energy in proportion as the distance is smaller. This effect is termed the induction of electricity. In consequence of this law, if an electrified body, charged with either species of electricity, be presented to an unelectrified or neutral body, the electrical condition of the different parts of the neutral body is disturbed. The electrified body induces a state of electricity contrary to its own, in that part of the neutral body which is nearest to it, and consequently a state of electricity similar to its own in the remote part. Hence the neutrality of the second body is destroyed by the action of the first; and the adjacent parts of the two bodies, having now opposite electricities, will attract each other. It thus appears, that the attraction which is observed to take place between electrified bodies and those that are unelectrified, is merely a consequence of the altered state of those bodies, resulting directly from the law of induction.

II. The hypothesis which naturally suggests itself for the explanation of the phenomena above stated, is that of a very subtile, imponderable and highly elastic fluid, pervading all material bodies, and capable of moving with various degrees of facility through the pores or actual substance of different kinds of matter. In some, as in those we call conductors or non-electrics, it moves without any apparent obstruction; while in others, as in those we call non-conductors or electrics, it moves with difficulty. Moreover, as the phenomena appear to indicate the agency of two kinds of fluid, we shall, for the present, assume the existence of two specics, and shall speak of these under the names of the vitreous and the resinous electricities. They must each have, when separate, the same general properties as have already been enumerated above;

while, in relation to each other, there must be a complete contrariety in their nature, so that, when combined together, their action on the bodies in their immediate vicinity shall cease. And it is when existing in this state of union or neutrality, that bodies are said to be in their natural state as respects electricity. We shall now proceed to compare the suppositions we have made with the facts, as presented to us by nature, and developed by experiment.-a. Facts connected with excitation. From various causes (of which the friction of surfaces is one), the state of union in which the two electricities naturally exist in bodies is disturbed: the vitreous electricity is impelled in one direction, while the resinous is transferred to the opposite; and each manifests its peculiar powers. When accumulated in any body, each fluid acts in proportion to its relative quantity, i. e., to the quantity which is in excess above that which is still retained, in a state of inactivity, by its union with electricity of the opposite kind. Thus, when glass is rubbed with a metallic amalgam, a portion only of the electricities at the two surfaces is decomposed: the vitreous electricity resulting from this decomposition attaches itself to the glass; the resinous to the amalgam. What remains in each surface undecomposed, continues to be quite inert.-b. Facts connected with distribution. Both of these fluids, being highly elastic, their particles repel one another with a force which increases in proportion as their distance is less; and this force acts at all distances, and is not impeded by the interposition of bodies of any kind, provided they are not themselves in an active electrical state. It has been deduced, from the most careful analysis, that this force follows the same law with that of gravitation: viz. that its intensity is inversely as the square of the distance. The mode in which the electricity imparted to a conducting body, or to a system of conductors, is distributed among their different parts, is in exact conformity with the results of this law, as deduced by mathematical investigation. While the particles of each fluid repel those of the same kind, they exert an equally strong attraction for the particles of the other species of electric fluid. This attraction, in like manner, increases with a diminution of distance, and follows the same law as to its intensity: viz. that of the inverse ratio of the square of the distance. This force, also, is not affected by the presence of any intervening body.-c. Facts connected with transferrence. Since the

two electricities have this powerful attraction for each other, they would always flow towards one another, and coalesce, were it not for the obstacles thrown in their way by non-conductors. When, instead of these, conducting substances are interposed, they enter into union with great velocity, producing, in their transit and confluence, several remarkable effects. When once united, their powers remain dormant, until again called into action by the renewed separation of the fluids.-d. Facts relating to attraction and repulsion. The repulsion which is observed to take place between bodies that are insulated, and charged with any one species of electricity, and other bodies similarly charged, is derived from the repulsive power which the particles of this fluid exert towards those of their own species; and the attractions between bodies differently electrified, is derived from the attractive power of the vitreous particles for those of the opposite kind. In all cases, the movements of electrified bodies represent the forces themselves which actuate the particles of the developed electricities they contain.—e. Facts relating to induction. Wherever one of the electricities exists in an active state, it must repel all the particles of the same electricity in all surrounding bodies, and attract those of the opposite species. Thus the law of induction is seen to be a direct consequence of the hypothesis we are considering. Thus far we have proceeded upon the hypothesis of two distinct electric fluids. It was, however, discovered by Franklin, that it is equally easy to account for all the phenomena, on the supposition of their resulting from the agency of a single electric fluid. This theory supposes, that the sin gle agent in question, and which we shall call the electric fluid, is highly elastic or repulsive of its own particles, the repulsion taking place with a force varying inversely as the square of the distance; that its particles attract and are attracted by the particles of all other matter, following the same law of the inverse square of the distance; that this fluid is dispersed through the pores of bodies, and moves through them with various degrees of facility, according as they are conductors or non-conductors. Bodies are said to be in their natural state, with regard to this fluid, when the repulsion of the fluid they contain of a particle of fluid at a distance, is exactly balanced by the attraction of the matter in the body for the same particle; and, under these circumstances, they exhibit no electrical phenomena.

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But if subjected to certain operations, as friction, the equilibrium is destroyed, and they acquire more or less than when in their natural state. Whenever they acquire a quantity of fluid greater than in their natural state, they are said to be positively electrified, or to be electrified plus, and present the phenomena ascribed to what was called vitreous electricity.— When, on the other hand, there is a quantity less than what is required in order to be in their natural state, they are said to be negatively electrified, or to be electrified minus; in which case they correspond with the state of resinous electricity. The state of positive electricity, then, consists in a redundance of the electric fluid, or in matter over-saturated with this fluid; that of negative electricity, in a deficiency of fluid, or in matter undersaturated, or, what may be considered the same thing, in redundant matter. In considering the mutual electrical actions of bodies, the portions in which the matter and the fluid mutually saturate each other," need not be taken into account, since their actions, as we have seen, are perfectly neutralized; and we need only attend to those of the redundant fluid and the redundant matter. When a body contains more than its natural proportion of electric fluid, the surplus will, by the repulsive tendency of its particles, overflow and escape, unless prevented by insulation, until the body is reduced to its neutral state. When under-saturated, the redundant matter will attract fluid from all quarters, from which it can receive, until it is again brought to its natural state. The mutual recession of two positively electrified bodies is a direct consequence of the redundance of the electric fluid contained in each, this fluid being attracted to the matter by its attraction for it in both bodies; and the fluid in one being repulsive of the fluid in the other, the bodies are necessarily impelled in the direction of the repulsion. In the same manner, the mutual attraction between two bodies, one of which is electrified plus, and the other minus, is the immediate effect of the attraction of the redundant fluid in one for the redundant matter in the other, and vice versa; for this attraction is mutual. The mutual recession of two bodies, negatively electrified, does not appear to be accounted for upon the Franklinian theory. In order to do this, therefore, it has been found necessary to append to it the following provision: that particles of simple matter, or bodies unsaturated with the electric fluid, are mutually