GALVANIS M.

Origin of the Discovery.-Galvani Professor at Bologna.-Accidental Effect on Frogs.-Ignorance of Galvani.-His Experiments on the Frog.-Accidental Discovery of the Effect of Metallic Contact.-Animal Electricity.-Galvani Opposed by Volta.-Volta's Theory of Contact Prevails.-Fabroni's Experiments.-Invention of the Voltaic Pile.-La Couronne de Tasses.-Napoleon's Invitation to Volta.-Physiological Effects of the Pile.-Anecdote of Napoleon.-Decomposition of Water.-Cruickshank's Experiments.-Davy commences his Researches.-Effect of Chemical Action discovered.-Ritter's Secondary Pile.-Calorific Effects of the Pile.-Hypothesis of Grotthus.-Davy's celebrated Bakerian Lecture.-Prize awarded him by the French Academy.-His Discovery of the Transferring Power of the Pile in Chemical Action.-His ElectroChemical Theory-Decomposition of Potash and Soda.-New Metals, Potassium and Sodium.— Discovery of Barium.-Strontium, Calcium, and Magnesium.-Rapid Discovery of the other new Metals.-Dry Piles.

GALVANIS M.

THE investigation of the mechanical phenomena of material substances has been, in modern works, conducted by resolving these effects into two principal divisions; those in which the bodies exhibiting them are at rest, and those in which they are in motion. As applied to solid bodies, these divisions have been respectively denominated STATICS and DYNAMICS; and, as applied to fluids, HYDROSTATICS and HYDRODYNAMICS. Electricity being assumed to be a physical agent, having the properties of an elastic fluid, and capable, like the grosser solids and fluids, of being maintained in a state of equilibrium by the mutual action and reaction of antagonist forces, or of moving in definite directions, and forming currents of greater or less intensity, the analysis of its effects would naturally be conducted by means of the same classification; and, accordingly, that division of the science in which the electric fluid is considered in a state of equilibrium or repose, and in which the physical conditions on which such equilibrium depends are investigated, would be denominated ELECTRO-STATICS, while that in which the effects of currents of electricity are considered, would be called ELECTRO-DYNAMICS.

REST being in its nature more simple than MOTION, and the cases of forces mutually destructive of each other's influence, and therefore productive of equilibrium, being more simple than those in which motion ensues from the combined action of forces differing from each other in various respects, it was natural that, in every part of physics, the principles of statics should be first established and understood. Such has been accordingly the course which the progress of discovery has taken in other branches of natural philosophy, and electricity is not an exception to it. All the phenomena which have been hitherto adverted to in this notice belong properly to ELECTRO-STATICS. In all of them the electric fluid is contemplated in a state of equilibrium; or if its motion be occasionally considered, it is only in sudden and momentary changes from one state of equilibrium to another. Thus, when a Leyden jar is char

The terms STEREO-STATICS and STEREO-DYNAMICS would be preferable.

ged, the positive electricity accumulated on the inner surface of the glass is maintained there, in spite of the tendency it has to escape in virtue of its selfexpansive property, by the attraction of the negative electricity accumulated on the external surface. When a communication is made between the internal and external surfaces by a metallic wire, this state of equilibrium ceases; the positive fluid of the inner surface runs along the wire in one direction, and the negative fluid of the external surface runs along it in the other direction, until each neutralizes the other, and a new state of equilibrium is established by the actual combination of the two fluids. If this change occupied a sensible interval of time, and it were required to investigate the effects which would be produced during that interval either on the jar and wire, or on any bodies which might be within their influence, the question would properly belong to ELECTRO-DYNAMICS; but in fact the discharge, as it is called, or the transition from the one state of equilibrium to the other, is instantaneous, and the same may be said of all the phenomena which form the subject of the preceding

pages.

In the commencement of this notice, the frequent influence of circumstances, apparently fortuitous, on the progress of discovery in the sciences, has been mentioned. It would be difficult, either in the history of the sciences or of the political growth of states, to find a more signal example of this than was offered by the discovery of that powerful instrument of physical investigation, the VOLTAIC PILE. "It may be proved," says M. Arago, "that this immortal discovery arose in the most immediate and direct manner from a slight cold with which a Bolognese lady was attacked in 1790, for which her physician prescribed the use of frog-broth."

Galvani was professor of anatomy at Bologna. At the period just mentioned, it happened that several frogs, divested of their skins, and prepared for cooking the broth prescribed for Madame Galvani, lay upon a table in the laboratory of the professor, near which at the moment stood an electrical machine. One of the professor's assistants, being employed in some process in which the machine was necessary, took sparks occasionally from the conductor, when Madame Galvani was astonished to see the limbs of the dead frogs convulsed with movements resembling vital action. She called the attention of her husband to the fact, who repeated the experiment, and found the motions reproduced as often as a spark was taken from the conductor. This was the first, but not the only or chief part played by chance in this great discovery.

Galvani was not familiar with electricity. Had he been so, he would have seen in the convulsions of the frog evidence of nothing more than a high electroscopic sensibility in the nerves of that animal, and an interesting example of the known principle of electrical induction. But luckily for the progress of science, he was more an anatomist than an electrician, and beheld with sentiments of unmixed wonder the manifestation of what he believed to be a new principle in the animal economy, and, fired with the notion of bringing to light the proximate cause of vitality, engaged with ardent enthusiasm in a course of experiments on the effects of electricity on the animal system. It is rarely that an example is found of the progress of science being favored by the ignorance of its professors.

Chance now again came upon the stage. In the course of his researches he had occasion to separate the legs, thighs, and lower part of the body of the frog from the remainder, so as to lay bare the lumbar nerves. Having the members of several frogs thus dissected, he passed copper hooks through part of the dorsal column which remained above the junction of the thighs, for the convenience of hanging them up till they might be required for the purposes of experiment. In this manner he happened to suspend several upon the iron

balcony in front of his laboratory, when, to his inexpressible astonishment, the limbs were thrown into strong convulsions. No electrical machine was now present to exert any influence.

If the supply of capital facts be occasionally due to chance, or to the Being by whom what is miscalled chance is directed, it is to the operation of the faculties of exalted minds that the development of the laws of nature is due if rude lumps of the natural ore of science be now and then thrown under the feet of philosophy, the discovery of the vein itself, its depth and direction, its quality and value, the separation of the precious metal it contains from its baser elements, the demonstration of its connexion with the phenomena of nature, and its adaptation to the uses of life, are all and severally the work of that noble faculty of intellect, that image of his own essence, which the Creator of the universe has impressed upon man, and which is never more worthily exercised than in the investigation of those laws of the material world, in all of which, whether they affect the vast bodies of the universe, or the imperceptible molecules of those around us, there is ever conspicuous a provident care for the wellbeing of his creatures.

In the convulsions of the frog, suspended by a copper wire on an iron rail, Galvani saw a new fact, and soon discovered that the circumstance on which it depended was the simultaneous contact of the metals with the nerves and muscles of the animal. He found that the effects were reproduced whenever the muscles touched the iron while the nerves touched the copper, but that contact with the copper alone did not produce them. He next placed the body of the animal upon a plate of iron, and touching the plate with one end of a copper wire, brought the other end into contact with the lumbar nerves. The convulsions followed as before. Galvani inferred from these and other similar experiments and observations, that the conditions under which the phenomenon was produced were, that a connexion should be made between the nerves of the animal and the muscles with which those nerves were united by a continued line or circuit composed of two different metals; and he explained this singular effect by assuming, hypothetically, that, in the animal economy, there exists a natural source of electricity; that, at the junction of the nerves and muscles, the natural electricity is decomposed; that the positive fluid goes to the nerve, and the negative to the muscle; that the nerve and muscle are therefore analogous to the internal and external coating of a charged Leyden jar; that the metallic connexion made between the nerve and the muscle in the experiments above-mentioned serves as a conductor between these opposite electricities; and that, on making the connexion, the same discharge takes place as in the Leyden experiment.

This theory fascinated for a time the physiologists. The phenomena of animal life had been ascribed to an hypothetical agent, which passed under the name of the "nervous fluid." The Galvanic theory consigned this term to the obsolete list; and electricity was now the great vital principle, by which the decrees of the understanding, and the dictates of the will, were conveyed from the organs of the brain to the obedient members of the body. Those who know how passionate is the love of a theory which appears to give a satisfactory account of effects otherwise mysterious, and how much more gratifying to the amourpropre it is to be able to connect effects with supposed causes, than to be compelled to view the former as the real limits of our knowledge, will understand the reluctance with which the Bolognese school and its distinguished leader would surrender a theory so dazzling as animal electricity; nevertheless it was doomed soon to fall under the irresistible assaults of physical truth directed against it by a giant intellect, which, though located in a little village of the Milanese, belonged to mankind.