a substance of such amazing splendour, it is no wonder that an inferior degree of light should in these circumstances be unperceivable.

As to the faculæ, or brighter parts of the sun, we are at a loss for their origin. It may in general be remarked, that though we have obtained an experimental proof, that the luminous matter acquires some degree of shade, when forming the sides of an excavation, yet it is uncertain if this be merely the effect of position, and much more so, if any different modification of position could ever dispose it to put on a brighter or more fulgid appearance. Yet, after all, may not these faculæ, &c. depend on some irregularities in the bright surface of the sun? For may not the luminous matter, by being agitated by the same cause to which the spots owe their origin, though in a less degree, have its surface perpetually disturbed, and made irregular, and thus give occasion to a variety of light and shade, sufficient, perhaps, to produce the phenomena under consideration? And does not this conjecture receive further confirmation, when we consider, that these faculæ, &c. are found only in that zodiac within which the spots appear, and that they always abound most in the neighbourhood of the spots themselves, or where spots recently have been? For in those undisturbed regions of the sun that lie towards his poles, and where no spots ever appear, we never discover any diversity of appearance.

Thus Dr. W. has endeavoured to give a general idea of the production, changes, and decay of the solar spots, considered as excavations in the body of the sun; a thing which seems to be established from the observations described in the first part of this paper. But concerning the nature of that mighty agency, which occasions those amazing commotions in the luminous matter, or concerning the density, viscidity, and other qualities of this matter, or the manner in which it is disturbed in the middle zone only, and not at the polar regions, and many such other questions, he freely confesses, that they far surpass his knowledge.

Experiments and Observations on the Gymnotus Electricus, or Electrical Eel. By HUGH WILLIAMSON, M.D. of Philadelphia. [1775.]

A SEA-FARING man brought to this city a large eel, that had been caught in the province of Guiana, a little to the westward of Surinam. It had the extraordinary power of communicating a painful sensation, like that of an electrical

shock, to people who touched it, and of killing its prey at a distance. The eel was three feet seven inches long, and about two inches thick near the head. On a transient view it resembled one of our common eels both in shape and colour; but its head was flat, and its mouth wide, like that of a cat-fish, without teeth.

On touching the eel with one hand, Dr. W. perceived such a sensation in the joints of his fingers as he received on touching a prime conductor or charged phial, when no circle was formed; or such as he had received, when a few sparks of the electric fluid have been conveyed through his fingers only. On touching the eel more roughly, he perceived a similar effect in his wrist and elbow. Touching the eel with an iron rod, 12 inches long, he perceived the like sensation in the joints of the thumb and fingers with which he held the metal. While another person provoked the eel by touching it, Dr. W. put his hand into the water at the distance of three feet, and felt such a sensation in the joints of his fingers as when he had touched the eel, but not so painful. Some small fishes were thrown into the water where he was swimming; he killed them immediately, and swallowed them. A cat-fish, that was at least one inch and a half thick, was thrown into the water where the eel was swimming; he killed it also, and attempted to swallow it, but could not. To discover whether the eel killed those fish by an emission of the same fluid with which he affected the hand when touched, Dr. W. put his hand into the water, at some distance from the eel; another cat-fish was thrown into the water; the eel swam up to it, but presently turned away, without offering any violence. After some time he returned; when, seeming to view it for a few seconds, he gave it a shock, by which it instantly turned up its belly, and continued motionless; at that very instant Dr. W. felt such a sensation in the joints of his fingers as in the former experiment.

A great variety of other experiments were made by two persons, one touching the eel near its head, the other putting his hand into the water, or touching it near the tail, forming a communication at the same time between their hands, which were out of the water, by pieces of charcoal, rods of iron or brass, a piece of dry wood, glass, silk, &c. The uniform result of all these experiments was, that whatever usually conveys the electrical fluid, would also convey the fluid discharged by the eel; and vice versâ, a brass chain, that had very many links in it, would not convey it, unless when the shock was severe, or the chain tense.

From the above experiments it appears, 1. That the Guiana eel has the power of communicating a painful sensation to animals that touch or come near it. 2. That this effect depends entirely on the will of the eel; that it has the power of giving a small shock, a severe one, or none at all, just as circumstances may require. 3. That the shock given, or the painful sensation communicated, depends not on the muscular action of the eel, since it shocks bodies in certain situations at a great distance; and since particular substances only will convey the shock, while others, equally elastic or hard, refuse to convey it. 4. That the shock must therefore depend on some fluid, which the eel discharges from its body. 5. That as the fluid discharged by the eel affects the same parts of the human body that are affected by the electric fluid; as it excites sensations perfectly similar; as it kills or stuns animals in the same manner; as it is conveyed by the same bodies that convey the electric fluid, and is not conveyed by other bodies that do not convey the electric fluid; it must also be the true electrical fluid; and the shock given by this eel must be the true electrical shock.

An Account of the Gymnotus Electricus. By JOHN HUNTER, F.R.S.-[1775.]

THIS fish, on the first view, appears very much like an eel, from which resemblance it has most probably got its name; but it has none of the specific properties of that fish. This animal may be considered, both anatomically and physiologically, as divided into two parts; viz. the common animal part, and a part which is superadded, viz. the peculiar organ. The first, or common animal part, is so contrived as to exceed what was necessary for itself, in order to give situation, nourishment, and most probably the peculiar property to the second. The last part, or peculiar organ, has an immediate connection with the first; the body affording it a situation; the heart, nourishment; and the brain, nerves, and probably its peculiar powers. For the first of these purposes, the body is extended out in length, being much longer than would be sufficient for what may be called its progressive motion. For the real body, or that part where the viscera and parts of generation lie, is situated, with respect to the head, as in other fish, and is extremely short; so that, according to the ordinary proportions, this should be a very short fish.

The organs which produce the peculiar effect of this fish,

constitute nearly one half of that part of the flesh in which they are placed, and perhaps make more than one third of the whole animal. There are two pair of these organs, a larger and a smaller; one being placed on each side. The large pair occupy the whole lower or anterior, and also the lateral part of the body, making the thickness of the fore or lower parts of the animal, and run almost through its whole length; viz. from the abdomen to near the end of the tail. It is broadest on the sides of the fish at the anterior end, where it incloses more of the lateral parts of the body, becomes narrower towards the end of the tail, occupying less and less of the sides of the animal, till at last it ends almost in a point. These two organs are separated from one another at the upper part, by the muscles of the back, which keep their posterior or upper edges at a considerable distance from one another; below that, and towards the middle, they are separated by the air-bag; and at their lower parts they are separated by the middle partition.

The small organ lies along the lower edge of the animal, nearly to the same extent as the other. Its situation is marked externally by the muscles which move the fin under which it lies. Its anterior end begins nearly in the same line with the large organ, and just where the fin begins. It terminates almost insensibly near the end of the tail, where the large organ also terminates.

The structure is extremely simple and regular, consisting of two parts; viz. flat partitions or septa, and cross divisions between them. The outer edge of these septa appear externally in parallel lines nearly in the direction of the longitudinal axis of the body. These septa are thin membranes, placed nearly parallel to one another. Their lengths are nearly in the direction of the long axis, and their breadth is nearly the semidiameter of the body of the animal. They are of different lengths, some being as long as the whole organ. Their breadths differ in different parts of the organ. They are in general broadest near the anterior end, answering to the thickest part of the organ, and become gradually narrower towards the tail, however they are very narrow at their beginnings or anterior ends. Those nearest the muscles of the back are the broadest, owing to their curved or oblique situation on these muscles, and get gradually narrower towards the lower part, which is in a great measure owing to their becoming more transverse, and also to the organ becoming thinner at that place. They have an outer and an

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inner edge. The outer is attached to the skin of the animal, to the lateral muscles of the fin, and to the membrane which divides the great organ from the small; and the whole of their inner edges are fixed to the middle partition formerly described, also to the air-bladder, and three or four terminate on that surface which incloses the muscles of the back. These septa are at the greatest distance from one another at their exterior edges near the skin, to which they are united; and as they pass from the skin towards their inner attachments, they approach one another. The distances between these septa will differ in fishes of different sizes. In a fish of two feet four inches in length, I found them to be about of an inch distant from one another; and the breadth of the whole organ, at the broadest part, about an inch and a quarter, in which space were 34 septa. The small organ has the same kind of septa, in length passing from end to end of the organ, and in breadth passing quite across: they run somewhat serpentine, not exactly in straight lines. They appear to be so close as even to touch. In an inch in length there are about 240, which multiplies the surface in the whole

to a vast extent.

The nerves in this animal may be divided into two kinds; the first, appropriated to the general purposes of life; the second, for the management of this peculiar function, and very probably for its existence. They arise in general from the brain and medulla spinalis, as in other fish; but those from the medulla are much larger than in fish of equal size, and larger than is necessary for the common operations of life. The nerve which arises from the brain, and passes down the whole length of the animal (which I believe exists in all fish), is larger in this than in others of the same size, and passes nearer the spine. This nerve is as singular an appearance, as any in this class of animals; for surely it must appear extraordinary, that a nerve should arise from the brain to be lost in common parts, while there is a medulla spinalis giving nerves to the same parts. It must still remain one of the inexplicable circumstances of the nervous system. In this fish, as well as in the torpedo, the nerves which supply the organ are much larger than those bestowed on any other part for the purposes of sensation and action; but it appears to me, that the organ of the torpedo is supplied with much the largest proportion.

The engraving is a section of the whole thickness of the fish near the upper part. The skin is removed as far back as the