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opened, and the issuing steam condensed in the bell, and in a few seconds the gold leaves diverged to a great extent, with positive electric action, even without removing the insulated plate of the condenser. But when the steam was directed to the wire only, outside of the bell, no electric action was observable, for the very obvious reason that the condensation of steam was too trilling to show it.
When the water last used was drawn off, and replaced by a saturated solution of common salt, and afterwards boiled as in the previous case, no trace of electric action could be discovered. After this fact was ascertained, the boiler was cleansed of its saline contents, and filled with distilled water, which was boiled till the steam again arrived at a pressure of thirty-one inches of mercury; but in this case the electroscope could not be affected. When, however, the water was reduced to about the same quantity as at first, the condensed steam gave electrical indications. Several other variations of the experiments were made with various results, though in all cases where electrical indications were afforded, they were of the positive action. Dr. Schafhaentl was, however, led to suppose that the success of the experiments depended entirely upon that state of the escaping steam which caused a peculiar fluttering noise, which happened only when the boiler was charged with about an inch and a half deep of water; for when the steam ceased to make that fluttering noise, although at a pressure of thirty-two inches of mercury, would even cause the previously diverged gold leaves to speedily collapse.
This peculiar noise, which appeared to be so essential to the production of electricity by steam, Dr. S. supposes to be owing to the sudden boiling of the water, and the conversion of a portion of it into a fine spray; under which circumstances the issuing steam deposited a large quantity of water in the bell glass, which often ran in streams from its lower edge. Insulation of the boiler did not appear to affect the results of the experiments, the electrical action being to the same amount whether the apparatus was insulated or not. “ A proof,” says Dr. S., “that the electricity of the steam developed in the glass bell could not be contained* in the steam during its passage through the three-inch long metallic jet of the boiler, as all the electricity would have been deposited in ibis narrow metallic passage.” Dr. Š. is led to suppose that a partial condensation of the steam into mist, for instance, is not sufficient to produce electric action, as its conversion into water appeared to be requisite for electrical developement. From this circumstance the Doctor supposes that he has discovered some clue to direct him to the cause why certain clouds only, are capable of producing thunder storms. He says that“ a common cloud, consisting only of moisture, seems to be analogous to a pure jet of steam in the glass bell, both consisting of minute hollow water globules, or bubbles, leaving only a small deposit of moisture in the glass bell, or in the air, which finally collects into sinall drops of rain. But when the steam depo
• Of course Dr. S. meant that it was not sensible in that tube.
sits rapidly a great quantity of liquid water, which in a thunder cloud produces those well known heavy showers, electricity is set free in great quantities, so that a jet of issuing steam from Marcet's boiler, in three seconds produced the same effect on the gold leaves of the electroscope as a feeble spark from an electric machine, with a glass plate of nine inches diameter, produced in damp weather.”
The general tenor of these speculations iu the analogy, appears to be perfectly correct; at least it is in accordance with our own views on the subject; but we are very far from entertaining the opinion that the steam, whilst passing through “the three-inch long metallic jet,” was not electrical. For such an opinion, if correct, would at once extinguish the idea, “that a partial condensation of the steam into mist, is not sufficient to produce electric action.” For if the law of electric developement holds good in one stage of condensation, it must also hold good in every other stage. And, although the misty steam produced no sensible electric action in the experiments in question, that was no reason for supposing that no such action was present in the steam within the jet; but on the contrary, it would lead us to infer that the steam within the jet pipe was electro-negative, and its conversion into mist within the bell, brought it to its natural electric state of neutrality: and that a further condensation lessened its electric capacity another stage, by which means it became electro-positive, as shown by the experiments. These are the theoretical views we have always entertained on this interesting subject, whether the steam be produced and recondensed artificially, or by the usual processes of nature; and hence it is that we cannot entertain the idea of any dense cloud being in a negative electric state, unless influenced by the repulsive electric action of some other vicinal cloud more densely electrical than itself.
An experimenter would easily discover that Dr. S.'s electroscope was not of the most delicate kind, or its indications would not have been compared to those produced by a “spark;" for it is well known that a spark, however feeble, would immediately spoil a delicate gold leaf electroscope.
Although by some of the experiments already described, Dr. S. could not detect electric action when the boiler was charged with salt water, it is stated by that gentleman, that, in subsequent experimeuts, "if the water in the boiler was saturated with common salt, or with sulphate of lime, and even a slight excess of sulphuric acid, the angle between the diverging gold leaves remains the same as if distilled water was used.” Hence, he very justly insers, “ that the observed free positive electricity, in this case, was solely attributable to the sudden condensation and separation of water from steam, &c.” And he might as justly have stated, that all electro-positive actions from steam or the vapour of water, depend on condensation. Hence, generally, whether the vapours be produced slowly or rapidly, it is first electro-negative, next, by a certain degree of condensation, electro-neutral, and, finally, electro-positive by every future degree of condensation.-EDIT.
ON VOLTAIC PILES.
Having so many solicitations from various quarters for information on several points in the history of electricity, and also respecting certain pieces of apparatus, especially in voltaic electricity, it would be difficult to know where to begin to give satisfaction to all parties. However, as some of our correspondents are anxious to know how to construct the dry electric pile, and others wish to have information respecting the earliest experiments in galvanism, we shall endeavour to satisfy both inquiries on these connected subjects, by giving the best data that we can procure from the accounts given by the authors themselves of their respective discoveries.
It appears that in the year 1767, a work, entitled “ The General Theory of Pleasures,” was published by M. Sultzer, in which the author describes the following experiment:"Take two pieces of metal, one of silver, the other of lead, and bring their edges into contact with each other; and while thus connected, place them both on the tongue: a taste will be experienced similar to that produced by vitriol of iron (sulphate of iron). But no trace of any such taste is perceived by the application of either metal individually.” Sultzer does not say whether he placed on the tongue each metal separately whilst in contact with the other, or whilst entirely alone; but it may possibly be useful to some readers to know, that the experimenter will find no difference in the effect, whether the metal placed on the tongue be in contact with another metal or not, provided this latter metal be not also in contact with the tongue, or some other moist part of the body. Under the latter circumstance, however, even hy holding the second metal with the finger and thumb, if perspiring, or otherwise moistened, the peculiar taste will be felt. Although the experiment of Sultzer is of that class which has received the title
galvanic," it was not till about twenty-four years afterwards, viz., 1791, that Professor Galvani made his discovery, which led to this branch of electricity. The following account of this discovery, given by M. Volta in two letters to Cavallo, will always be found interesting.
The subject of these letters, says M. Volta, is that of animal electricity, discovered by Dr. Galvani, and publised by him in a work entitled, “ Aloysii Galvani de Viribus Electricitatis in Motu Musculari Commentarius. Bononiæ, 1791." This subject, under the name of galvanism, has given occasion to several important discoveries, having been very much culttvated by many respectable philosophers, and by none more than by those of England.
Dr. Galvani having cut and prepared a frog, so that the legs hung on one side of the spine of the back, separate from the rest of the body, solely by the crural nerves laid bare, he found that there were produced very quick motions ni the legs, with spasmodic contractions in all the muscles, whenever a spark was taken from the prime-conductor of an electric machine, not on the body of the
animal, but on every other body, and in every other direction; this part of the animal being placed at a considerable distance from the conductor, and in certain circumstances. These were, that the animal, thus dissected, should be in contact, or very nearly so, with some metal, or other good conducting substance of a sufficient ex. tent, and still better between two such conductors, the one of them being directed towards the extremity of the said legs of the animal, or some one of the muscles, the other towards the spine, or the nerves. It is also of great advantage that one of these, called the nervous and the muscular conductors, but preferably the latter, should have a free communication with the floor. It is in this position especially that the legs of the animal receive violent shocks, leap up and down rapidly on each spark from the conductor of the machine, though it may be pretty far distant, and though the discharge be not made on either the nervous or muscular conductor, but on some other body, likewise distant from them, and having another communication for transmitting such a charge, as on some person placed in an opposite corner of the room.
Such was the first step, which led him to the fine and grand discovery of an animal electricity, properly so called, appertaining not only to frogs and other cold-blooded animals, but also to all warmblooded animals, as quadrupeds, birds, &c.; a discovery which makes the subject of the third part of the work quite new and interesting.
It was chance that presented to M. Galvani the phenomenon just described, but at which he was more astonished than he needed to have been, had he given due attention to the effects of electric atmospheres. Yet who could have believed that an electric current, so weak as not to be rendered sensible by the most delicate electrometers, was capable of affecting so powerfully the organs of an animal, and of exciting in its members, cut off many hours before, motions as strong as those of the living animal, as the vigorous springing of the legs, the leaping, &c., not to mention the most violent tonic convulsions?
M. Volta endeavoured to determine the least electric force requisite to produce these effects, as well in a living isolated frog as in one dissected and prepared as before-mentioned, which M. Galvani had omitted to do. M, Volta chose the frog in preference to every other animal, because it is endued with a very durable vitality, and is also very easy to prepare. He also made trial of other small animals for the same purpose, and with nearly the same success. Hence he found, that for the living and entire frog the electricity of a simple middle-sized conductor was sufficient, when it was only capable of giving a very feeble spark, and to raise Henly's electrometer to 5° or 6. When he used a Leyden phial of a middle size, a much weaker charge produced the same effect, viz., such as gave not the least spark, and was quite insensible to the quadrant electrometer, and hardly sensible to Cavallo's electrometer.
All this was for a whole and isolated frog; but for one dissected
and prepared in different ways, especially after Galvani's manner, where the legs are attached to the dorsal spine only by the crural nerves, a still much weaker electricity, whether of the conductor or of the Leyden phial, the fluid being obliged to pass through the narrow passage of the nerves, never failed to excite convulsions, &c. Hence, then, we have, in the legs of the frog attached to the dorsal spine only by the bare nerves, a new kind of electrometer; since the electric charge which, giving no signs by other the most delicate electrometers, gives evident tokens of it by this new means, by what may be called the animal electrometer.
But if, after these experiments, we ought not to be surprised at those of Galvani described in the first and second parts of his work, how can we avoid being so at the very novel and marvellous ones in the third part? by which he obtains the same convulsions and violent motions of the members, without having recourse to any artificial electricity, by the sole application of some conducting arc, of which one extremity touches the muscles, and the other the nerves or the spine of the frog, prepared in the manner aforesaid. This conducting arc may be either wholly metallic or partly metallic, and partly some of the imperfect conductors, as water, or one or more persons, &c. Even wood, walls, the floor, may enter into the circuit, if they be not too dry. The bad conductors, however, do not answer so well, and only for the first moments after the preparation of the frog, as long as the vital forces are in full vigour; after which the good conductors only can be used with success, and soon after we can only succeed with the most excellent ones, namely, with conducting arcs wholly metallic. Galvani successfully extended these experiments, not only to many other cold-blooded animals, but also to quadrupeds and birds, in which he obtained the same results, by means of the same preparations; which consist in disengaging from its coverings one of the principal nerves, where it is inserted into a member susceptible of motion, in arming this nerve with some metallic plate or leaf, and in establishing a communication, by help of a conducting arc, between this arming and the depending muscles. Thus he happily evinced the existence of a true animal electricity in almost all animals. It appears proved, indeed, by these experiments, that the electric fluid has a continual tendency to pass from one part to another of a living organised body, and even of its lopped members, while they retain any remains of vitality; that it has a tendency to pass from the nerves to the muscles, or vice versa, and that muscular motion is due to a like transfusion, more or less rapid. Indeed it seems that there is nothing to be objected either to the thing itself, or to the manner in which M. Galvani explains it, by a kind of discharge similar to that of the Leyden phial.
M. Galvani following up the idea he had formed, after his experiments, and to follow in every point the analogy of the Leyden phial and the conducting arc, pretends that there is naturally an excess of the electric Auid in the nerve, or in the interior of the muscle, and a cor