To him is due the first clear description of the electrical lobes situated in the torpedo’s brain and of its relation to the eighth pair of nerves distributed throughout the hexagonal columns, which latter received also from him a very extended notice in the above-named work. The fifth ramification of nerves was first observed by Carus, and the most valuable investigation relative to the fourth and last important group of nerves directly connected with the electrical organs was made by the celebrated Italian professor, Carlo Matteucci.
References.—Larousse, “Dict. Univ.,” Vol. IX. p. 867; C. Matteucci, “Traité des Phénomènes Electro-Phys.,” Paris, 1844, pp. 283–318; Geoffroy St. Hilaire at A.D. 1803.
Another author, Delle Chiaje, likewise gave a description of the rhomboidal sinus-shaped protuberance which he calls lobo pagliarino (straw-coloured lobe), and which he considers as formed of one mass but does not admit its important connection with the electrical organs.
A.D. 1811.—Poisson (Siméon Denis), a very able French scientist, communicates to the “Institut des Mathématiques et Physiques” and publishes at Paris under the caption “Traité de Mécanique,” his analytical observations of the electric phenomena which, it has been truly said, actually establish a new branch of, and is the best elementary work extant upon, mathematical physics. One of his biographers remarks that Poisson’s object was “to leave no branch of physics unexplored by aid of the new and powerful methods of investigation which a school, yet more modern than that of Lagrange and Laplace, had added to the pure mathematics.”
As shown, notably by Sir David Brewster in his able article on “Electricity” in the eighth “Encycl. Brit.” (Vol. VIII. p. 531), and by Noad, in his “Manual” (London, 1859, pp. 15, 16):
“Poisson adopted as the basis of his investigations the theory of two fluids, proposed by Symmer and Dufay, with such modifications and additions as were suggested by the researches of Coulomb. He deduced theorems for determining the distribution of the electric fluid on the surfaces of two conducting spheres, when they are placed in contact or at any given distance, the truth of which had been established experimentally by Coulomb before the theorems themselves had been investigated. On bodies of elongated forms, or those which have edges, corners or points, it is shown as a consequence of the theory of two fluids that the electric fluid accumulates in greater depths about the edges, corners or points than in other places. Its expansive force, being therefore greater at such parts than elsewhere, exceeds the atmospheric pressure and escapes, while at other points of the surface it is retained.”
In the latter connection Mary Somerville remarks:
“There can hardly be a doubt but that all the phenomena of magnetism, like those of electricity, may be explained on the hypothesis of one ethereal fluid, which is condensed or redundant in the positive pole, and deficient in the negative; a theory that accords best with the simplicity and general nature of the laws of creation; nevertheless, Poisson has adopted the hypothesis of two extremely rare fluids, pervading all the particles of iron, and incapable of leaving them. Whether the particles of these fluids are coincident with the molecules of the iron, or that they only fill the interstices between them, is unknown and immaterial. But it is certain that the sum of all the magnetic molecules, added to the sum of all the spaces between them, whether occupied by matter or not, must be equal to the whole volume of the magnetic body.... M. Poisson has proved that the result of the action of all the magnetic elements of a magnetized body is a force equivalent to the action of a very thin stratum covering the whole surface of a body, and consisting of the two fluids—the austral and the boreal, occupying different parts of it; in other words, the attractions and repulsions externally exerted by a magnet are exactly the same as if they proceeded from a very thin stratum of each fluid occupying the surface only, both fluids being in equal quantities, and so distributed that their total action upon all the points in the interior of the body is equal to nothing. Since the resulting force is the difference of the two polarities, its intensity must be greatly inferior to that of either” (J. C. Wilcke at A.D. 1757, “Conn. of the Phys. Sci.,” 1846, s. 30 pp. 308, 309).
The “Mémoires de l’Institut” for 1811 contain Poisson’s very able papers showing the manner in which electricity is distributed on the surfaces of bodies of various figures and the thickness of the stratum of electricity existing throughout these bodies. Mrs. Somerville further observes of work already cited (s. 28):
“Although the distribution of the electric fluid has employed the eminent analytical talents of M. Poisson and M. Ivory, and though many of their computed phenomena have been confirmed by observation, yet recent experiments show that the subject is still involved in much difficulty. Electricity is entirely confined to the surface of bodies; or, if it does penetrate their substance, the depth is inappreciable; so that the quantity bodies are capable of receiving does not follow the proportion of their bulk, but depends principally upon the form and extent of surface over which it is spread; thus the exterior may be positively or negatively electric, while the interior is in a state of perfect neutrality.” (Consult J. Farrar, “Elem. of Elect. Magn. and Electro-Magn.,” 1826, pp. 50–56.)