might occupy some months very pleasantly; but the delay of a few days here is the loss of a season, and we cannot reckon on more than two months in the year for such purposes."

"MY DEAR SIR,

"FORT FRANKLIN, GREAT Bear Lake, "March 23. 1826.

"In consequence of an imperfect, but very interesting, Indian report of Captain Parry's wintering on the coast, and which Captain Franklin is desirous of investigating, I have another opportunity of writing to you this season. The particulars of the report, when ascertained, will be transmitted to Mr Barrow, from whom you may get them.

“I mentioned, in a former letter, that a formation of lignite occurs in this quarter. The lignite has a slaty structure, thinnish, or only moderately thick; and, when exposed to the atmosphere, cracks into forms generally nearly rectangular. Some portions, which are rather thick slaty, with a flat conchoidal fracture in the small, bear a very near resemblance to the slaggy mineral pitch or bitumen so common in the limestone forma tion of Slave River (zechstein?). It is distinguished from it when put in the fire.

"In the more common form of the lignite, the surface of the slates is more dull and earthy, of a brownish-black colour, but yielding a shining streak. These slates are entirely composed of fragments, having all the appearance of charred wood united together by a paste of more comminuted woody matter, mixed perhaps with a minute portion of clay. In the paste, there are some minute perfectly transparent crystals, having the form of compressed four sided prisms, and sometimes of tables. The fibrous structure of the woody fragments is fine, and the lustre resembles that of fresh well-made charcoal of brick. The struc

ture is evidently exogenous. The fragments are generally

small, but, when several inches in diameter, their layers of structure are waved and curved, as if they had been knots, which of course would not so easily break down as the other portions. One of my specimens .shews a small grain, either of resin or of amber; and I have picked out of another a membranous substance, which has all the appearance of a portion of Ulva montana (Bot. App. Franklin's Journey) common

here at the present time. I inclose this minute specimen, which has already suffered some diminution in the course of my examination of it. Muriatic acid produced no change in it; but I was afraid to try the nitric acid, lest it should destroy it.

"When put into the fire the lignite burns without flame, and emits a very disagreeable stench, unlike that of either peat or of sulphur. The combustion does not cease when the coal is removed from the fire, but goes on slowly, until there is only a brownish-red ash remaining, not one-tenth of the original bulk of the specimen.

"The beds of lignite lie on the east side of Bear Lake River, where it joins the Mackenzie, are in the aggregate six or seven yards thick, and are covered by a thick bed of loose sand. They were on fire when Sir A. Mackenzie discovered the river (in 1789), and have continued burning ever since. At the distance of a few hundred yards up the Bear Lake River, there are some thick beds of a coarse, bluish-grey, earthy looking sandstone (very like that on the north side of the Calton Hill), dipping at a small angle under the lignite. They were not seen in actual contact. On the opposite side of Bear Lake River, which is 200 yards wide, a craggy hill of (carboniferous ?) limestone rises abruptly to the elevation of 400 feet. About 30 miles farther up Bear Lake River, and nearly east from its mouth, the stream cuts the base of another limestone hill, of similar form and height, belonging to a chain of (partly transition ?) hills, which runs N.W. and S. E. through a flat country. At the foot of the nearly vertical limestone, but separated from it by a small rivulet, there are thick horizontal beds of sandstone, resembling that at the mouth of Bear Lake River. Upon this. sandstone lie a number of thin beds of bituminous shale and sandstone, which weather easily. In the shale there are impressions of ferns (polypodiaceae), and in the slaty sandstone lepidodendra? I have had no opportunity of examining these rocks, excepting very cursorily, as we passed them in the boat, and occasionally snatched a specimen; but I purpose, if the snow disappears long enough before the opening of the navigation, to visit them carefully this spring. The finest sections on the banks of the river will be hid by accumulations of ice till the autumn."

On the Luminousness observed in the Eyes of Human Beings, and also in those of Cats, Dogs, Horses, and Sheep. By Dr CHARLES LUDWIG ESSER *.

APPEARAN

PPEARANCES of light, as is well known, are not uncommon in inferior animals, and the number of luminous animals in the sea is so great, that large tracts of the water's surface have been seen to be illuminated by them.

This phenomenon, however, is comparatively seldom observed in fishes, and the more rarely the higher we ascend in the scale of the animal kingdom, if under the denomination of luminousness, we understand the real evolution of light, and do not consider it as the reflection of the incident rays of light; for in this latter case the luminous appearance does not inhere in the animal body itself, but is in reality merely a reflection, which is totally different from the evolution of light in the inferior animals. A real phosphorescence is sometimes observed in the higher animals, and even in human beings, particularly in their excrementitious fluids. The light of the eggs of the lizard, the luminousness of the perspired matter in man and horses, the irradiation of light in cats and other animals, from the stroking of their hair, and finally the phosphorescent quality of human urine, have been frequently observed.

On most of these various kinds of light, I have neither performed experiments myself, nor have I collected the facts of others; the present memoir being chiefly devoted to an examination of the light or luminousness of the eyes in human beings and inferior animals.

The more perfectly to accomplish this object, I some years ago performed a series of experiments, that led to an important result.

Having brought a cat into a room half darkened, I observed that the eyes of the animal when opposite the window, and in a certain direction to myself, sparkled very brilliantly, which phenomenon suddenly vanished, when I, either by the motion of my head, changed the direction of my eyes to those of the cat, or the

* Karsten's Archiv, b. viii. heft iv.

animal, by moving its eyes to and fro, brought them into a different position. In a situation wherein I could best observe the eyes of my cat, I caused the room to be slowly darkened, by gradually closing the window-shutters. The light of its eyes became weaker, and vanished entirely as soon as the room, on the place where the cat was situated, became absolutely dark. Incident rays of light were always necessary to produce the luminousness of the eyes.

I wrapped another cat in a cloth, but left the head uncovered, whereby I was able to handle the animal as I had a mind, and place it in any situation I chose. In this cat what I have just stated was confirmed. I placed it in such a position that its head, at the distance of a few steps, was directed towards the window, by which means I could lighten or darken the room at pleasure. I now permitted a few rays of light to fall through the window into the room, in such a manner, that the place where the cat was present was illuminated; and I placed myself in such a direction towards the window, that my eyes were in a straight line with those of the animal, so that I saw the light of its eyes very distinctly, which light, as in the former experiment, suddenly vanished when I turned my head, or the cat turned its eyes. At the moment when my eyes were directed in the manner just mentioned, I observed a most beautiful green light; ́but when they were out of this direction, the cat's eyes had their usual appearance. By the turning of my head, or by any other arrangement I chose, by which I intercepted the incident rays, I could at pleasure cause sometimes the one eye of the cat, sometimes the other, and sometimes both together, to shine. If I intercepted the incident rays of light from the left half of the head, the right eye became luminous, and conversely. In these experiments, I observed quite distinctly that the light of my cat's eye emanated from the pupil, the eye itself being lightened only in proportion to the dilatation of that part of it. By suddenly admitting a strong glare of light into the room, I produced a contraction of the pupil; and when I suddenly rendered the room somewhat dark, a small round luminous point first appeared in the eye, and that point enlarged according as the pupil was dilated. The pupil of the eye of these animals being thus dilated in imperfect darkness, so that the iris seems to encircle the pupil as a small ring, and the sclerotic in cats

being scarcely visible, may be the reason why it is believed that the whole eye of the cat is luminous, although its light is, nevertheless, only in proportion to the dilatation of the pupil.

The dilatation of the pupil in twilight is, however, not the only cause of the light of the eyes; but the light surrounding the animal being fainter, also assists us in perceiving with greater distinctness the light as it is more vividly reflected from their eyes; for, if we suddenly illuminate the chamber in which there is a cat, there remains nothing but a luminous brightness where there was formerly a beautiful yellowish green light.

The light of my cat's eyes seemed to be more vivid when she opened them wide from apprehension, or looked around her attentively; whence Treviranus observed, that the eyes of cats sparkled most when the animals were in a lurking position, or in a state of irritation. That author says,

"The light of the cat's eyes appears most conspicuous when she is in a lurking position,-when she is attracted by any unusual appearance, or when irritated. In the first two instances, the light is faint and dull: in the last instances, it darts forth in intermittent scintillations, and at those moments when the light is most vivid, there are accompanying movements of the eyes." That the light of the eyes of animals appears bright ́er in a state of irritation than in a state of quiescence, seems to originate in this, that the eyes of all animals, as well as those of man, appear brighter in violent rage, and sparkle more, than in a quiescent state. This, in man, seems to arise from an increased secretion of the lachrymal fluid on the surface of the eye, by which fluid the light of the eye is undoubtedly rendered more brilliant. Treviranus farther observes, "The eyes of the cat shine also where no rays of light penetrate, and the light must in many, if not in all, cases proceed from the eye itself." Before performing the above experiments, I entertained the same opinion with Treviranus, and made many fruitless experiments with cats in the dark, before I abandoned the position. The light must be brighter in proportion to the darkness of the place where the cat is. I soon renounced this opinion, when, in all the experiments I made on cats, in places absolutely dark, I did not discover the slightest trace of light in the eyes of these animals, let me irritate them as I could.