Bibliographical history of electricity & magnetism, chronologically arranged

by Unknown

Sect. III treats of the excitement produced by a simple metallic substance, or by homogeneous metallic parts (detailing the experiments of Aldini, Galvani, Berlinghieri, Lind, Pfaff and Volta).

Sect. IV discourses on heterogeneous metals. During his experiments in this line, which were aided by his elder brother, chance led him to a very interesting discovery. He found that the coatings of the nerve and muscle being homogeneous, the contractions may be produced when the degree of excitability is extremely feeble, provided the coatings of this nature are united by exciting substances, among which there is a heterogeneous one, having one of its surfaces covered by a fluid in a state of vapour. This observation, which was originally made at the commencement of 1796, surprised Humboldt so much that he instantly communicated it to Sömmering, Blumenbach, Hertz and Goethe. He had not as yet found recorded in the published works on galvanism any experiment the result of which had the smallest analogy with his discovery; and it was not until after the publication of the works of Pfaff on animal electricity that he became acquainted with any one similar to his own. There were, however, some differences, as he proves by several passages cited from the above author.

Sect. V relates to the classification of active substances into exciters and conductors of the galvanic fluid.

Sect. VI treats of experiments on the comparative effects of animal and vegetable substances employed in the galvanic chain.

Sect. VII describes, in a tabular form, the conducting substances, and those by which the galvanic fluid is insulated. In the employment of very long conductors, it was not possible for Humboldt to remark any interval between the instant when the muscle contracts and the moment the contact of the conductor takes place, the muscle and nerve being from two hundred to three hundred feet distant from each other. This announces a celerity of twelve hundred feet per second. The effect would be the same, should the conductors even be from ten thousand to twenty thousand feet in length. Thus Haller, in his physiology, ascribes to the nervous fluid a swiftness sufficient to enable it to run over a space of nine thousand feet a second. The calculation of Sauvages is carried to thirty-two thousand four hundred feet in the same space of time; and what is still infinitely more surprising, its celerity is estimated by the author of the essays on the mechanism of the muscles at five hundred and seventy-six millions of feet (upward of one hundred thousand miles) in the above space of a second of time. It ought here to be noticed that the great differences in these calculations arise from the different kinds of experiments on which they are founded.

Sect. VIII proves that the nerve which is intended to excite contractions in a muscle should be organically united with it, and it deals with the effects of galvanism upon vegetables, aquatic worms, insects and fishes.

Sect. IX describes the effects of galvanism upon amphibious animals, referring to the observations of Nollet, Rosel, Haller, Spallanzani, P. Michaelis and Herembstads.

Sect. X treats of the all-important effects of galvanism upon man, and makes allusion to the experiments of Hunter, Pfaff, Fowler, Munro, Robison, Hecker, Carradori, Achard, Grapengieser, Schmuck, Ludwig, Creve, Webster and Volta. In speaking of the observations made by the last named upon the tongue, he observes that some idea of them had been given thirty years before, in Sulzer’s work entitled “The New Theory of Pleasures,” published in 1767; and that if, at the above period, the consideration of the superficial situation of the nerves of the tongue had led to the artificial discovery of a nerve, the important discovery of metallic irritation would have been made in the time of Haller, Franklin, Trembley, Camper, and Buffon. How great a progress would not this revelation have made if the above philosophers had transmitted to us, thirty years ago, the theory and experiments which we leave to our successors?

Volta having singled out the differences, in point of savour, which result from galvanic experiments on the tongue according to the nature and disposition of the coatings, Humboldt repeated these experiments and added to them several of his own, with a nearly similar result. His different trials, however, having failed to produce any contraction of the tongue, appear to have established the truth of the ancient assertion of Galen, confirmed by Scarpa, namely, that the nerve with which the tongue is supplied by the third branch of the fifth pair is exclusively devoted to the sense of tasting, and that the ninth pair are exclusively destined for the motion of the tongue. This has been evidently proved by the galvanic experiments on the nerve in question.

The termination, in the pituitous membrane, of the nerves belonging to the organ of smelling, which originate in the first pair and in the first two branches of the fifth, together with the observation of the innumerable phenomena of sympathy between the organs of sight and those of smell and taste, had led to a presumption that, by galvanizing the nostrils, the smell would be affected. This supposition has not, however, been confirmed by any experiment.