tion. Fets of which there can be no loss of the electric matter, as Electricity there is in the case of the chain by the ring points. on Vegeta- Moreover, this metal cord or thread being capable of being untwisted and lengthened, there will be no occasion for transporting so often the electrical machine. It is almost needless to add, that this string or metallic cord, which is always insulated, may rest upon the same kind of supports with those which have been exhibited in OP and s of fig. 131. and 132. This method is simple, efficacious, and nowise expensive, and cannot be too much employed. 539 Easy me thod of applying elec tricity in this man ner. "If one wants to water either a parterre or common garden, beds and platforms of flowers, or any other plots in which are sown grain or plants of differ ent ages and kinds, no method is more easy and expeditions than the following: Upon a small carriage with two wheels there is placed a framed insulator in form of a cake of pitch and rosin, as we have mentioned before in N° 538. The carriage is drawn the whole length of the garden by a man or horse fixed to it. In proportion as you draw the carriage, the metallic cord winds itself upon a hobbin, which turns as usual. This last is insulated, either because the little apparatus that sustains the bobbin is planted in a mass of rosin (when you choose the axle to be of iron), or else because this moveable axis is a tube of solid glass. There must also be a support which serves to prevent the gold thread or the metallic cord from trailing on the ground, and thus dissipating the electricity; and, moreover, it serves for an insulator. To accomplish this last purpose, it is necessary that the ring into which it passes be of glass. One may likewise employ the insulators and supports marked OP and s, in fig. 131. and 132. If a gardener, mounted upon an insula. tor, holds in one hand a pump full of water, and with the other takes hold of a metallic cord, in order to transmit the electricity which comes from the conductor; in this case, the water being electrified, you will have an electrical shower; which falling on the whole surface of the plants which you want to electrify, will render the vegetation more vigorous and more abundant. A second gardener is to give additional pumps full of water to him who is upon the insulator, when he shall have emptied those he bolds; and thus in a little time you will be able to electrify the whole garden. This method takes hardly longer time than the ordinary one; and although it should be a little longer, the great advantages resulting from it will abundantly recompense the small additional trouble. "By repeating this operation several days successively, either upon seed sown or plants in a state of growth, you will very soon reap the greatest advantages from it. This operation, equally easy with the preceding described upon the subject of watering trees, has been put in practice with the greatest success. Several other 540 methods, answering the same purpose, might be deTo electrivised; but they are all of them pretty similar to that fy water kept in re- just described. servoirs, & c. "I cannot finish this article without mentioning tion. another method relative to the present object, although Effects of it be much less efficacious than the preceding ones. Electricity It consists in communicating to water kept in basons, on Vegetareservoirs, &c. (for the purpose of watering), the electric fluid, by means of a good electrical machine. To this end, one must plaster over with a bituminous cement all the interior surface of the bason destined to receive the water that serves for irrigation; the na ture of this cement answering the purpose of insulation, will prevent the electric fluid that communicates with the water from being dissipated; and the water thus charged with electricity will be the more fitted for vegetation. 541 the electric "If the deficiency of the electric fluid, or rather a Vegetables small quantity of it, is apt to be hurtful to vegetables, injured by a too great abundance of this matter will likewise shock. sometimes produce pernicious effects. The experiments made by Messrs Nairne, Banks, and other learned men of the Royal Society of London, prove sufliciently this truth. An electric battery, very strong, was discharged upon a branch of balsam still holding by its trunk. Some minutes after, there was observed a remarkable alteration in the branch, of which the less woody parts immediately withered, dropped towards the ground, died next day, and in a short time entirely dried up; at the same time that another branch of the same plant that had not been put under the electric chain, was not in the smallest degree effected. "This experiment repeated upon other plants showed the same effects; and it was remarked that the attrac tion, occasioned by a strong discharge of the electricity, produced an alteration different according to the dif ferent nature of the plants. Those which are less woody, more herbaceous, more aqueous, experience in proportion, impressions that are stronger and much more speedy in their operation. "A branch of each of the following plants, composing an electrical chain, it was observed by these able philosophers, that the balsam was affected by the discharge of the battery in a few moments after, and perished next day. The leaves of a marvel of Peru did not drop till the day following that; and the same phenomenon happened to a geranium. Several days elapsed before there was observed any fatal effect on the cardinal flower. The branch of a laurel did not show any symptoms till after the lapse of about 15 days, after which it died; but it was a full month before they perceived any sensible change on the myrtle; at the same time they constantly observed that the bodies of those plants and branches which had formed no part of the chain, continued to be fresh, vigorous, and covered with leaves in good condition *. Phil. "It hardly ever happens that the superabundance of Trans. the electric fluid existing in a small portion of the at- vol. ¿xiv. mosphere where a plant is situated, can be so great as that which took place by the explosion of the strong battery of Mr Nairne, directed particularly upon one branch; or if this should happen, it can only be upon a few individual plants in a very small number." ᏢᎪᎡᎢ . Animal Electricity. Animal Electricity. 542 The raia PART VII. DEVELOPEMENT OF ELECTRICITY IN ANIMALS. CERTAIN animals, which have been observed to communicate sudden and strange sensations by simple contact with their bodies, or even through the medium of other substances, without such contact, have been found to owe this property to the faculty of transmitting electrical shocks of greater or less intensity, a faculty which is exercised by the instrumentality of peculiar organs. One of these animals is well known under the name torpedo. of the torpedo. It is a fish of the ray kind, and denominated by naturalists the raia torpedo. It lives in the seas of the southern parts of Europe, and is also frequently found on the southern shores of this island. Its benumbing powers have been long known. The electrical nature of these powers was ascertained by Mr Walsh, in a paper addressed to Dr Franklin, from la Rochelle, the place where his observations were made, and inserted in the Philosophical Transactions for 1773. It is by touching the upper surface of the animal with one hand, and the lower with the other, that the shocks are most readily felt. They are extremely frequent, especially when the animal is dying, though then much feebler. They take place both when the animal is in the water and in the air; and are particularly powerful in the moment of separating him from the surface of the water, or bringing him in contact with it. The most remarkable movement in the body of the animal accom. panying these shocks is a drawing in of the eyes, which at other times are very prominent. The electrical organs of the animal occupy a large space between the vital or gans and the fins on each side, and they consist of cylindrical bodies, or rather prisms of various hexagonal irregular sections, generally resembling the cells of a honeycomb. The longitudinal direction of these bodies is right across the thickness of the animal, reaching nearly to the skin at both ends, being separated from it by two thin fascia. These columnar bodies consist of numerous partitions, about 150 in an inch, between which a gelatinous substance is interposed. The columns them selves are about of an inch in diameter. The number of them forming an organ on each side has been sometimes found to be 470. The identity of the shock communicated by this animal with electricity is proved by its passing through all conducting substances, and them only, as well as by the kind of sensation produced. It has not however been seen to generate the electric spark, or the snapping noise in its passage through air. The anatomy of this animal is described by Mr John Hunter, in another paper contained in the same volume. In order to shew how the electrical nature of the shocks given by the torpedo is sufficiently consistent with the absence of all electrical sparks, and of snapping noise, Mr Cavendish shews, by an able series of experiments and of calculations, contained in the Philosophical Transactions for 1776, that it is sufficiently explained by the great quantities of contrary electricities generated in the parts of the animal which are in opposite directions, together with the small intensity of the charge. The intensity, or tendency to equilibrium by transmission, is that power which is indicated by the different electrometers; but this intensity dimi nishes in proportion to the surface over which any charge is diffused. It will not now pass through an equal interval of air between two conducting surfaces; yet it will display the powerful effects of the amount of transmission by other tests, such as the shock given to an animal placed in the electrical circuit, and the mechanical action exerted on substances placed in its way. Now, when the torpedo produces a charge in the electrical organs of its own body, by a voluntary exertion, this charge has for its surface all the thin membranes forming the septa into which the columnar bodies are divided. As the charge of which a battery is susceptible is also in proportion to the thinness of the partitions, this circumstance is, in the structure of the torpedo, highly favourable to the accumulation of such a large quantity of a charge, with so little intensity, as fully to account for it not exhibiting the phenomena now alluded to, and not even being communicable between the links of a metallic chain, notwithstanding the strength of the shock which it gives to an animal body. Mr Cavendish made experiments with an artificial torpedo, first of wood and then of leather, soaked with sea water. He made an electric charge of a given intensity, and a given quantity, to pass from the upper to the lower surface, also through the human body, to try the strength of the shock through a metallic chain, and making trials of the electric spark and snapping noise. From the reduction of the latter phenomena, in proportion as his charge approached in circumstances to that which may be supposed to exist in the living animal, he drew the inference, that the deficiency of these phenomena was no evidence against the electrical nature of the shock of the torpedo. Another anomaly had presented itself, in the transmission of the shock through the human body, even while the surfaces of the animal were connected by the water in which the animal was immersed. This also was satisfactorily explained by experiment; and to this object the artificial torpedo was principally applied. Another electrical animal, possessed of still greater powers, is the gymnotus electricus, which is found in the rivers of South America. It is a large animal, nearly of the shape of an eel, and is called the electric eel. Its length is from three to four feet in those which have been described from actual examination, but it is said that some are much larger. The vital organs are situated close to the head, and are of no greater length than the head itself: the anus being in a part which we should call the neck of the animal. The rest of the length is occupied with the electric organs, the back-bone with its muscles and tail, the spinal cord, the great sympathetic nerves, and the air bladder. The electric organs consist of two pairs, one |