imagined by many, that the indivi- to occasion contractions. Gold and zinc, the first the most perfect of the metals, the other an imperfect one, operate together very powerfully in producing contractions; while gold and, the next most perfect metal, silver operate very feebly. It would seem, there fore, that the more similar the me tals are, which are thus used, the less is the power arising from their combination. Two pieces of the same metal, but with different portions of alloy, are still more feeble than gold and silver; and the power of such pieces becomes less and less, in proportion as they approach each other in point of purity. From these facts it has been inferred, that, if any two pieces of the same metal were to possess precisely the same degree of purity, they would, if used together, be entirely inert, in regard to the excitement of muscular contractions; in confirmation of which, many persons have asserted, that they have never observed muscles to move from the employment of two such pieces of metal, or of one piece of metal having the same fineness through its whole extent. Others, however, upon the authority of their observations, have maintained the contrary: and to the testimony of these I must add my own, as I have frequently seen muscular motions produced not only by a single metal, but likewise by charcoal alone. Nor will credit be denied me on this head, after I have pointed out certain practices, by which any one of those substances may at pleasure be made to produce contractions. The most proper way of mentioning these practices, will, perhaps, be to relate in what manner they came to my knowledge. I one day placed a piece of silver, and another of tin-foil, at a small distance from each other, upon the crural nerve of a frog, and then applied a bent silver probe between them, with the view of ascertaining, whether contractions would arise, agreeably to Mr. Volta's declaration, from the influence passing through a por. a portion of the nerve without entering the muscles. Having finished this experiment, I immediately after applied the same probe between the silver coating of the nerve and the naked muscles, and was surprised to see these contract. A second and third application were followed by the same effects, but farther applications were of no avail. It then occurred to me that motions might re-appear, if I again toucbed the two coatings with the probe, and the event proved the conjecture to have been fortunate; for, after every application of the probe to, the two coatings, contractions were several times excited by it. The fact being thus established, that, under certain circumstances, contractions could be produced by silver alone, it next became a subject of. inquiry, whether this was owing to. any disposition of the muscles and nerve, which had been induced upon them by Mr. Volta's experiment, or whether, the condition of the muscles and nerve being unaltered by that experiment, the silver had gained some new property by coming into contact with the tin-foil. The point in doubt was soon deter-, mined, by applying the probe to a piece of tin-foil, which had no connection with any part of the animal; for, when this was done, it was again enabled to produce contractions. As, these experiments, how ever, frequently did not succeed when made upon other frogs, I afterwards varied the metals, aud found in consequence, that zinc, particularly if moistened, communicated an exciting power pretty constantly to silver, gold, and iron. If any of these metals were slightly: rubbed on the zinc, they almost always acquired such a power. It will, perhaps, be thought, from the last-mentioned circumstance, that, in every instance of motion being in this way produced, it was in truth owing to some part of one of the metals having been abraded by the other; so that, under the appearance of one metal, two were in reality applied. But it can scarcely be supposed, that, from touching the polished surface of tin-foil in the gentlest manner with the smooth round end of a silver probe, any part of the former metal was carried away by the latter; and even when friction was used, as the zinc was much harder than the gold and silver, it is not probable that it was in the least abraded by them. Besides, moisture, as I have already said, increases this effect of friction, though it lessens friction itself. The most powerful argument, however, in favour of my opinion, is another fact I discovered in pursuing this subject; which is, that an exciting power may be given to a metal by rubbing it on many substances beside another metal, such as silk, woollen, leather, fish-skin, the palm of the human hand, sealing-wax, marble, and wood. Other substances will, doubtless, be hereafter added to this list. As the metals while they were rubbed were held in my hand, which, from the dryness of its scarf-skin, might have afforded some resistance to the passage of small quantities of the electric fluid; and as the substances, upon which the friction was made, were either electrics, or imperfect conductors of electricity; I once thought it possible, that the metal subjected to the friction had acquired, by means of it,an electrical charge, which, though very slight, was still sufficient to act as a stimu[E2] lus lus upon the nerves to which it was communicated. But that this was not the case was afterwards made evident, by the following experiments and considerations. 1. A metal, rendered capable by friction of exciting contractions, produced no change upon Mr. Bennet's gold-leaf electrometer. 2. The interposition of moisture does not, in any instance I know of, increase the effect of friction in exciting the electric fluid. In some instances it certainly lessens this effect. But moistened substances, when rubbed by a metal, communicate to it the capacity of producing contractions, much more readily than the same substances do when dry. 3. If my hand, from being an imperfect conductor, had occasioned an accumulation of electricity in the metal which was rubbed, a greater effect of the same kind ought certainly to have been produced by insulating the metal completely; which is contrary to fact. 4. I placed a limb of a frog, properly prepared, upon the floor of my chamber; if a severe frost had not prevailed when I made this experiment, I should have laid it upon the moistened surface of the earth. I then raised from the muscles, by means of an electric, the loose end of the nerve, and touched it with the rubbed part of a piece of metal; but no contractions followed. To be convinced that this was not owing to any want of virtue in the metal, I kept the same part of it still in contact with the nerve, while I applied another part to the muscles; immediately upon which contractions were excited. 5. Admitting now the limb of an animal to be in such an experiment completely insulated, and that the metal actually becomes electrical from the friction it undergoes,surely a very few applications can only be required to place them both in the same state with respect to the electric fluid; and when this happens, all motions depending on the transflux of that fluid must necessarily cease. I have found, however, that a piece of metal which has been rubbed will excite contractions, after it has been many times applied to the limb. In one instance, vigorous contractions were occasioned by the 200th application; and if I had chosen to push the experiment farther, I might certainly have produced many more. I may mention also, as connected with this fact, that I have frequently observed a piece of metal to excite motions, an entire day after it had been rubbed. What I have said will, probably," be thought more than sufficient to prove, that metals, after being rubbed, do not produce muscular contractions by means of any disengaged electricity they contain. If my opinion were now asked, respecting the mode in which friction communicates such a power to them, I should say, that the part which has been rubbed is so far altered, in some condition or property, as to be affected differently, by the fluid exciters, from a part which has not been rubbed; in short, that the rubbed part becomes, as it were, a different metal. There are two facts, besides those already mentioned, which support this conjecture. The first is, that when I have endeavoured to give an equal degree of friction to the two parts of the metal which I applied to the muscle, and its nerve, little or no motion Was was excited by it; so that it is reasonable to suppose, that, if precisely the same degree of friction were given to both the parts, no contractions would ever be produced by them, when used in this way. The second is, that, although only one part of the metal be rubbed, still, if both the muscle and nerve be coated with some other metal, the application of the rubbed metal between these similar coatings will not be followed by motions; which, however, will immediately be produced, by touching the naked muscle and nerve with the same piece of metal. But, whether any part of my reasoning upon this head be admitted as just or not, it must yet be granted, as I think I cannot be mistaken respect ing the facts which have been mentioned, that very slight accidents may give the power of exciting contractions to a single metal, which had it not before; and that we may hence easily account for the discordant testimonies of authors upon this point. Hitherto I have spoken only of the effects of friction upon metals. But to conclude this part of my subject, I must now remark, that charcoal, though from its friability not very fit for the experiment, may yet be rendered capable by the same means of producing contractions, without the assistance of any of the metals. My next and last objcet is to enquire, whether the influence, which in all these experiments immediate ly excites the muscles to act, be electrical or not. The points of difference between any two species of natural bodies, even those which, from the similarity of some of their most obvious qualities have once been thought the same, are found, upon accurate ex amination, greatly to exceed in number those of their agreement. When, therefore, two substances are known to have many properties in common, while their differences are few, and none of these absolutely contradict such a conclusion, we infer with considerable confidence, that they are the same, though we may not be immediately able to explain why their resemblance is not complete. After Mr. Walsh, for instance, had discovered, that the influence of the torpedo was transmitted by all the various bodies which are good conductors of the electric fluid, philosophers made little hesitation in admitting them to be one and the same substance, though some of their apparent diffe rences could not then be accounted for. In like manner, the inquirers into the nature of the influence, the effects of which are so evident in Mr. Galvani's experiments, have very generally, and in my opinion justly, allowed it to be electrical, on the ground that its conductors and those of electricity are altogether the same. To this, however, an objection has been made by Dr. Fowler, which, if well founded, would certainly prove them to be different substances; for he has asserted that charcoal, which is so good a conductor of electricity, refuses to transmit the influence, upon which the motions in Mr. Galvani's experiments depend. In reply, I shall only say, that Dr. Fowler must have been unfortunate with respect to the charcoal he employed; since all the pieces I ever tried, and I have tried many, were found to conduct this influence. Other arguments have likewise been urged against the identity of the two influences; all of which, [* E 3] how however, excepting one, I shall decline discussing, as they either are of little importance, or have not been stated with sufficient precision. The objection I mean is, that in none of the experiments with animals, prepared after the manner of Mr. Galvani, are those appearances of attraction and repulsion to be observed, which are held to be the tests of the presence of electricity. My answer to it is, that no such appear ́ances can occur in Mr. Galvani's experiments, consistently with the known requisites for their success, and the established laws of electri'city. For, as it has been proved, that there is naturally no disengaged electric fluid in the nerves and muscles of animals, I except the torpedo and a few others, no signs of attraction and repulsion can be looked for in those substances, before the application of metals or charcoal; and after these have been applied, the equilibrium of the influence, agreeably to what has been already shewn, is never disturbed, unless means for its restoration be at the same time afforded. Neither then ought signs of attraction and repulsion to be in this case presented, on the supposition that the influence is electrical; since it is necessary for the exhibition of such appearances, that bodies, after becoming electrical, should remain so during some sensible portion of time: it being well known, for example, that the passage of the charge of a Leyden phial, from one of its sur faces to the other, does not effect the most delicate electrometer; sus pended from a wire or other substance, which forms the communication between them. "Such are the observations I mean at present to submit to the consider ation of this Society, respecting the influence which incites the muscles of animals to contract, in Mr. Galvani's experiments. Observations on the Maritime Alps; from Beaumont's Travels through them. THINKING that some general THIN deductions from the principal facts, or phenomena, mentioned in the course of this work may be expected of me, especially with respect to the theory of the formation of their regular surface of the earth, at least of that wonderful part of it which I have so repeatedly explor ed, I have ventured to annex a few observations, which appear to me to merit the particular attention of philosophers, as likewise the consequences which I think might be drawn from them. I do not, however, mean to speak of what relates to the first and great revolution experienced by our globe at the formation of its continents: that is, at the epoch when the waters covered it about two thousand four hundred and fifty toises, and which is nearly the present elevation of some of the granitic peaks of the Alps, as Mont Blanc, Mont Rose, &c. In short, of the time when they were totally submerged by that element, and formed themselved under that fluid, either by effect of crystallization or precipita. tion. I therefore only intend to touch on the phenomena which relate to the last immersion experienced by our continent, and which appears to have been partial. I. From the immense atterrissements, or land-accumulations, already formed, and which are continually increasing at the mouth of 1 the |