large quantity of bright points (fig. 24) are then seen, which, like shooting stars, suddenly arise and disappear after a rapid motion, in various straight and curved lines. On close attention, it will be found that every light point is accompanied by a shade at the opposite side of the field of vision, and that also between the small, larger but less bright points are slowly moving. These larger points are very distinctly seen after violent exertion, particularly after lifting a weight: they move from the extreme margin of the field of vision towards the middle, and are in a straight or bent direction, always accompanied by a shade at the opposite side; the nearer they come to the middle, the less distinct and shining do they appear, and the less dark are their shadows. As they are visible only as long as the eyes are held open, and as they require a strong and equal light, in order to be seen, they must be considered as differing from the bright points described above, as far as these evidently depend on the different state of the various points of the retina, whilst the phenomenon in question is caused by external bodies, with reference to the retina, viz., according to Dr. Purkinje's opinion, by free blood-globules in the aqueous humour; which, according to their different distances from the crystalline lens, are seen of different size and distinctness.

XI. Luminous Rings. This phenomenon, which is sufficiently known to be caused by lateral pressure on the eye, has been carefully examined by Dr. Purkinje: the following are the results of his experiments:

1. If the observer makes an effort, as if to look at something very near, the slightest pressure produces the luminous ring; whilst, on looking at a distance, the pressure must be considerably increased.

2. The rings, as well as the places of insertion of the optic nerves, are most vivid in the morning, and the proximate cause of both phenomena appears to be identical, viz.; pressure on the retina.

3. If a piece of white paper is held in the inner angle, and whilst the eye is as much as possible directed towards it, the observer presses, with a small conical piece of wood, on the external side of the globe, near the orbit, a great number of

concentric white and black lines are seen (fig. 25), similar to the appearance of fig. 20; they extend over the spot in the middle of the visual field (fig. 20), and are always parallel wherever the pressure may be exerted. On the paper there appears, at the same time, a large black circular spot, the centre of which is of a dark bluish green, or deep violet, similar to the eye of a peacock's tail, sometimes with fragments of the vascular figure (fig. 13). That side of the spot which is directed towards the middle of the field of vision, touches at the abovementioned parallel lines; the opposite side is bordered by a yellowish-white gleam, which, on increased pressure, reaches as far as the middle of the black spot.

4. If by placing the piece of wood between the orbit and eye-lid, the pressure is exerted on the posterior point of the globe, the parallel lines are seen extending towards the middle of the field of vision, and terminating in a white semilunar streak, which, in its concavity, contains a small bright circle, and at the convex portion of which there is a brownish semilunar spot; both spots follow all the motions of the coloured eye, and turn round the centre of the field of vision as on an axis. If the pressure is increased, the coloured eye advances towards the white semilunar streak, so as to cover it entirely with the exterior of its middle portion, which remains as a white circular spot in the middle; the brown semilunar spot also disappears.

5. If the pressure on the globe is suddenly discontinued, the white circular spot as suddenly moves outwards, and in its stead a light-brown violet cloud remains, which is divided by a white streak into two parts, the upper of which is larger and darker; this cloud, especially the middle portion of it, generally remains for a considerable time, and greatly impedes clear vision.

6. The experiment in question shews also the coincidence of the two fields of vision; for if each eye is pressed at the corresponding place, the luminous rings are always seen to coincide.

7. If the eye is well covered during the experiment, the colours in the middle of the circular spot, as well as the margin round the periphery, are luminous; the concentric lines are very

indistinct, and of a faint gleam, and the yellowish-white glare at the outer side of the circular spot is black. On suddenly discontinuing the pressure, a bright luminous streak flashes from the inner towards the outer side.

Dr. Purkinje has evidently bestowed much time upon these experiments. It appears from some passages in his work, that he began, even in his boyhood, to amuse himself with some of the luminous appearances therein described. The study of physiology afterwards led him to an accurate and scientific inquiry, which he even pursued at the risk of health; for, although he in one passage of his work states that his experiments had not been injurious to his sight, the circumstance of his right eye being myopic, and the left near-sighted (amblyopic,) seems almost to contradict this assertion; we ourselves cannot, after a great number of experiments which we made before and since our perusal of Dr. Purkinje's work, withhold our conviction, that their frequent repetition may be attended with dangerous effects on the eyes. On the other side, it is indispensable that the experiments should be frequently repeated and varied; for at the commencement of the inquiry the observer must be quite unaccustomed to this new field of experiment. The condition of Dr. Purkinje's sight might further raise some doubts whether some of his experiments be not the effects of a morbid state, rather than depending the organization of the human eye.

We have not yet exhausted the experiments which this interesting pamphlet contains; some of those which are now omitted we shall have occasion to refer to in our succeeding papers*.

Since the preceding pages were printed, we have ascertained that the interesting experiment of § VIII. was first described by Steinbuch, in his Physiolie der Sinne, 1811.

DESCRIPTION OF THE HORNS OF THE PRUSSIAN ELK; DIFFERENCE BETWEEN THEM AND THOSE

OF THE AMERICAN MOOSE-DEER*.

BY WILLIAM WITTICH, Esq.

THE European elk and the American moose-deer are still considered by naturalists as belonging to the same species. Pennant and even Cuvier seem to have no doubt respecting their identity. Blumenbach and some other naturalists, indeed, are less decisive in their opinions; but their doubts rest on conjecture. The reason of this uncertainty seems to be, that a sufficient number of data have not yet been accumulated, to enable the promoters of science to form a clear and decisive judgment. The small number of facts which till now have been well established, refer to one side of the question; they regard almost exclusively the American moose-deer. This animal has often been brought to France and England from the transatlantic shores, where it is found in numerous herds; and on our continent it has been subjected to a more minute and accurate investigation. But the Scandinavian elk has perhaps never found its way to London or Paris; and what I dare not affirm positively of the Scandinavian elk, I believe I may assert with certainty of the Prussian-it was never seen in London or Paris.

The same may be observed respecting the collections of elkhorns: they consist almost exclusively of horns of the moosedeer; and what is not known to belong distinctly to that species is somewhat doubtful. That is the case with the collection in the British Museum; and if I may judge according to the drawings given in Cuvier's great work (Recherches sur les Ossemens Fossiles, tom. iv., pl. iv. 24-29), the Parisian collection likewise does not contain the horns of the Prussian elkdeer. As they, however, seem to exhibit in some points a different formation, I shall give here the description of a pair

Cervus Alces, Linn.

of Prussian elk-horns in the possession of Mr. Plaw, Modifort-court, Fenchurch-street.

This pair of Prussian elk-horns weighs twenty pounds and a half the larger weighs ten pounds and a half; the smaller

Horn of the Prussian Elk.

Horn of the Moose-deer.

h

7

The horn of the Moose-deer is copied from a sketch in the "Recherches sur les Ossemens Fossiles" of Cuvier, tom. iv., pl. iv., p. 70.

exactly ten pounds. The palmated part is divided by a deep and wide cut between the antlers 4 and 5. This cut terminates exactly over the stem.

The two palmated portions, formed by the above-mentioned cut, are not equal in extent; but the surface of the smaller contains more than one-third of the whole. The larger portion has four antlers, the smaller three. The neck, formed by the cut, and uniting both palmated partitions, is only four inches wide (from a to b). The breadth of the larger partition at the root of the antlers (from c to d) is ten, and that of the smaller (from e to f) is eight inches and a half. The length of the larger partition, from the root of the largest antler to the neck, is twelve, that of the smaller ten inches.

par

The largest antler of the larger partition is ten inches long; the others from seven to ten. The antlers of the smaller tition are from five to eight inches long. The circumference of the largest antler at the root is six inches and a half; at that place it is still somewhat palmated, but two inches further up it is round. The stem of the horn (from g to h) is six inches long; from the root of the stem (g) to the termination of the cut (a) are ten inches.

The two partitions do not lie in the same plain; but the