and growth. The roots of trees, particularly those in coppices, which are felled at stated periods, continue so long to produce and feed a succession of branches, that no experiments were required to prove, that it is not any defective action of the root which occasions the debility and diseases of old varieties of the apple and pear-tree. Mr. Knight next details a variety of experiments which he has made to ascertain the fact be is anxious to establish; and having formerly adduced arguments which are encontradicted, to shew that the sap of plants circulates through their leaves as the blood of animals circulates through their lungs; and having also shewn that grafted trees, of old and debilitated va rieties of fruit, became most diseased in rich soils, and when grafted on stocks of the most vigorous growth, which led him to suspect that in such cases more food is collected and carried up into the plant than its leaves can prepare and assimilate; and that the matter thus collected, which would have promoted the health and growth in a vigorous variety, accumulates and generates disease in the extremities of the branches and annual shoots, while the lower part of the trunk and roots remain generally free from any apparent disease. Hence he attributes the diseases and debility of old age in trees to an inability to produce leaves which can efficiently execute their natural office, and to some consequent imperfection in the circulating fluid. It is said, that the leaves are annually reproduced, and are therefore annually new; but there seems to be an essential difference between the new leaves of an old and of a young variety; and it is certain, that the external character of the leaf of the same variety at wo, and at twenty years old, is very dissimilar; and therefore to Mr. Knight it appears not improbable, that further changes will have taken place at the end of two centuries. "If (says he) these opinions be well-founded, and the leaves of trees be analogous to the lungs of animals, is it improbable that the natural debility of old age of trees and of animals, may originate from a similar source? This question Mr. Knight is not prepared to decide; but he believes it will be generally admitted, that the human subject is best formed for long life, when the chest is best formed to permit the lungs to move with the most freedom. And he has long observed among domesticated animals, that those

2

individuals longest retain their health and strength, and best bear excessive labour and insufficient food, in which the chest is most deep and capacious, proportionately to the length of current the circulating fluid has to run; and the same remark he suspects will be found generally applicable to the human species.

Mr. Macartney has communicated to this learned body some very interesting observations upon luminous animals: he examines the grounds on which the property of shewing light has been ascribed to certain animals, that either do not possess it, or in which its existence is questionable. He then gives an account of some luminous species, either inac curately described, or quite unknown: he next explains, either from his own observations, or from the information com. municated to him by others, many of the circumstances attending the luminous appearances of the sea: and he then describes the organs employed for the production of light in certain species; and lastly, he reviews the opinions which have been entertained respecting the nature and origin of animal light.

Mr. Macartney controverts the notions of many authors, who pretend to have witnessed the phenomena of light as belonging to animals, to which they certainly, he thinks, cannot belong. Flau gergues pretended to have seen earth. worms luminous in three instances; the body shone in every part, but most bril liantly at the genital organs. Now Mr. Macartney thinks it next to impossible, that animals so frequently before our eyes as the common earth-worm, should be endowed with so remarkable a property, without every person having ob served it. If they only enjoyed it during the moment of copulation, still it could not have escaped notice, as these creatures are usually found joined together in the most frequented paths in the gar den-walks. In the same way he treats many others; and then mentions some luminous animals discovered by Sir Jo seph Banks, Captain Horsburg, and himself: and he says, the zoophyte is the most splendid of the luminous inhabitants of the ocean. The flashes of light emitted during its contractions are so vivid as to affect the sight of the spectator. The luminous state of the sea between the tropics is generally accompanied with the appearance of a great number of marine animals, of various kinds, upon the surface of the water. In the Arabian Sea have been seen several

luminous

Juminous spots in the water, and when the animals, supposed to be the cause of them, were examined, they were found to be insects about the third of an inch in length, resembling in appearance the wood-louse. The insect, when viewed with the microscope, seemed to be formed by sections of a thin crustaceous substance. During the time that any fluid remained in the animal, it shone brilliantly like the fire-fly. Mr. Macartney supposes that this, and another mentioned as taken on a sandy beach, were monoculi. He notices many others that have from time to time come under his inspection; one of these, which he denominatesthe beroe fulgens, is a very elegant creature, changing its colour between purple, violet, and pale blue: the body is truncated before and pointed behind, but the exact form is difficult to assign, as it is varied by particular contractions, at the animal's pleasure. When this insect swam gently near the surface of the water, its whole body became occasionally illuminated in a slight degree: during its contractions, a stronger light issued from the ribs, and when a sudden shock was communicated to the water, in which several of these animals were placed, a vivid flash was thrown out. If the body were broken, the fragments continued luminous for several seconds, and being rubbed on the hand, left a light like that of phosphorus; this, however, as well as every other node of emitting light, ceased after the death of the animal. Mr. Macartney having noticed many other species, says, that his own observation, lead him to conclude, that the medusa scintillans is the most frequent source, light of the sea round this country, and likewise in other parts of the world. We are next informed, that the remarkable property of emitting light during life, is only met with among animals of th fou last classes of modern naturalists, viz. mollusca, insects, worms, and zoophytes. The mollusca and worms contain each but a single species; the phofas dactylus in the one, and the nereis nocticula in the other. Some species yield light in the eight following genera of inserts, viz. elater, lampyris, fulgora, pausus, scolopendra, cancer, lynceus, and limulus. The luminous species of the genera lampyris and fulgora, are more numerous than is gene. rally supposed. Among the zoophytes, the genera medusa, beroe, and pennatula, contain species which afford light, The only animals that appear to possess MONTHLY MAG. No. 211.

a distinct organization for the production of light, are the luminous species of lam. pyris, elater, fulgora, and pausus.

The light of the lampyrides proceeds from some of the last rings of the ab domen, which, when not illuminated, are of a yellow colour. The number of luminous rings varies in different species; and, as it seems, at different periods iu the same individual. Besides this luminous substance there are, in the common glow-worm, on the inner side of the last abdominal ring, two bodies, which to the naked eye appear more minute than the head of the smallest pin. They are lodged in two slight depressions, formed. in the shell of the ring, which is at these points particularly transparent. These, when examined, were found to be sacs, and contain a soft yellow substance. The light that proceeds from these sacs is less under the controul of the insect than that of the luminous substance spread on the rings: it is seldom entirely extinguished in the season that the glow-worm gives light, even during the day; and when all the other rings are dark, these sacs often shine brightly. In all the dissections made by Mr. Macartney, of luminous insects, he did not find that the organs of light were better, or differently supplied with either nerves or air-tubes, than other parts of the body. The power of emitting light likewise exists in some creatures which want nerves; a circumstance that strongly marks the difference between animal light and animal electricity. neral, the exhibition of light, in animals, depends upon the presence of a fluid matter, which in some instances is contined to particular parts of the body, and in others is diffused throughout the whole substance of the animal.

In ge

Mr. Macartney next notices the va rious explanations that have been given of the phenomena of animal light, and relates a number of experiments on the subject; and then gives the following conclusions, which are the result of the observations that he has made on the subject.

The property of emitting light is con fined to animals of the simplest organization, the greater number of which are inhabitants of the sea. The luminous property is not constant, but in general exists only in certain periods in particular states of the animal body. The power of shewing light resides in a particular substance, or fluid, which is some times situated in a particular organ, and

2 K

in

in others diffused throughout the animal's body. The light is differently regulated when the luminous matter exists in the living body, and when it is abstracted from it. In the first case it is inter. mitting with periods of darkness, is com. monly produced or increased by a mus. cular effort, and is sometimes absolutely dependent upon the will of the animal. In the second case, the luminous appear ance is usually permanent, until it becomes extinct, after which it may be restored directly by friction, concussion, and the application of warmth, which last causes operate on the luminous matter only indirectly by exciting the animal. The luminous matter, in all situations, is incombustible, and loses the quality of emitting light by being dried, or much beated. The exhibition of light, how. ever long it may be continued, causes no diminution of the bulk of the luminous matter. It does not require the presence of pure air, and is not extinguished by other gases. The luminous appear ance of living animals is not exhausted

by long continuance, or frequent repe titions, nor accumulated by exposure to natural light: it is therefore not dependent upon any foreign source, hut inheres as a property, in a peculiarly or ganized animal substance, or fluid, and is regulated by the same laws which govern all other functions of living be ings. The light of the sea is always produced by living animals, and most frequently by the presence of the medusa scintillans. When great numbers of this species approach the surface, they so times coalesce, and cause that snowy or milky appearance of the sea, which is so alarming to navigators. These ani. mals, when congregated on the surface of the water, can produce a flash of light like an electric corruscation. The tuminous property does not appear to have any connection with the economy of the animals that possess it, except in flying insects, which by that means discover each other at night, for the pur pose of sexual congress.

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2

Exhibition of the Works of British Artists, placed in the Gallery of the British Institu tion, Pall Mall, for Exbibition and Sale,

1811.

W

E shall now commence our observations on the pictures, which, from the limited space allotted to this department, must be brief.

N. 4. A Gypsy Woman telling a Young Woman Ber Fortune. By A. J. Oliver.

A.R.A.

Has been already noticed in our review of the last exhibition at Somerset-house; and a second inspection does not injure its character.

No. 7. Andromache imploring Ulyffes to spare the Life of her 'Son, G. Darve, A.R.Ä. Is in a similar situation. Justice, however, demands an acknowledgment, that it is among the best pictures in the exhibition.

No. 10. The Entombing of Christ. W. Hilton.

Never having been publicly exhibited before, and from its individual merits, deserves a more particular investigation. The principal figure, the Christ, is the best in the composition; is well-drawn, and excellently coloured is too formal and artificial, and the whole is crowded into too small a space. k

The grouping