and the latter in the several numbers through which our notices of the seventh, eighth, and ninth volumes of the Institute extended, it being in them that the observations of M. Ramond were first printed.

The next following articles contain very interesting accounts of the lives and writings of two eminent philosophers; viz. the celebrated navigator Bougainville, and our late worthy Astronomer-Royal, Dr. Maskelyne. The incidents in the career of the former are various and striking; we see him equally distinguished as a man of science, as a warrior both by sea and land, as a negotiator, and as the founder of a colony: but our limits will not allow us to give the details at length; and, as they are too interesting to admit of abridgment, we would rather pass them with this general notice than report them imperfectly. The same remark will apply to the memoir of Dr. Maskelyne. We shall therefore merely state that the former was born November 11. 1729, and died on the 31st August, 1811; and that the latter was born in 1732, and dicd Feburary 9. 1811.

(Part I.) MEMOIRS.

On the Distribution of Electricity at the Surface of conducting Bodies; First and Second Memoir. By M. POISSON. - We cannot attempt, in our report of these papers, to illustrate the mathematical processes which the author has adopted: but, as the theory on which he founds them, and some of the results that he has deduced, may be rendered intelligible in a few lines, we shall endeavour to exhibit them in the present article.

The theory of electricity, most generally admitted, is that which attributes all the several phænomena to two different fluids dispersed through all the bodies in nature; and in which we suppose that the particles of the same fluid mutually repulse each other, while they attract the particles of the other fluid. These attractive and repulsive forces follow the law of the inverse ratio of the square of the distance; and at the same distance the repulsive power is supposed equal to the attractive: whence it results that, when all the parts of a body contain an equal quantity of both fluids, they exercise no action on those contained in the bodies around them, and consequently no sign of electricity is in this case manifested. We therefore call this the natural state of the body; and, when this equilibrium is disturbed by any external cause, the body in which it takes place is said to be electrified. Those bodies which appear to exercise no species of action, but which admit of this fluid traversing them in every direction,as metals, are called conducting bodies; and those which op

pose

pose the progress of the fluid, as dry air, and many others, are called non-conductors: but the memoir before us is wholly occupied on the phænomena of the former class of bodies, either when considered in an isolated state or when they are brought near together and submitted to each other's mutual influence.

Let us imagine, says M. Poisson, a metallic body entirely immersed in dry air, and suppose a given quantity of one of the fluids to be introduced. In consequence of the repulsive force of its particles, and because the metal opposes no obstacle to its motion, we may conceive that the fluid thus added will be carried to the surface of the body; where it will be retained by the dry air that encompasses it. Coulomb has

in fact proved, by direct experiments, that no particle of electricity remains in the interior of an electrified conducting body, except that which belongs to its natural state; and that all the fluid which is added distributes itself at the surface, forming there an extremely thin layer, which does not penetrate sensibly below the surface, and of which the thickness at every point depends on the form of the body, so that the figure which it assumes ought to be that which appertains to a state of equilibrium.

The present writer demonstrates that the problem reduces itself to that of finding what ought to be the thickness of the fluid-layer in every point of the surface, in order that its entire action may be zero in the interior of the electrified body. This thickness will be greatest at the extremity of the greatest of the three axes, and least at the extremities of the shortest; and these thicknesses will be to each other as the length of the axes. Supposing, therefore, the depth of the layer to be very little, we may ascertain the distribution of the electricity at the surface of a spheroid but little different from a sphere; and this case, and that of the ellipsoid, are the only instances in which, in the present state of the analytical sciences, it would be possible to assign the variable thickness of the fluid.

By employing the formula for the attraction of spheroids, M. POISSON calculates the attraction of the fluid lamina on a point taken either in the interior or at the surface of the electrified body; and by this mode he has found that, at the surface of a spheroid but little differing from a sphere, the repulsive force of the fluid is proportional to its thickness, at each point: while it is the same in an ellipsoid of revolution, whatever may be the ratio of the axes. It follows, therefore, that, in bodies of the above forms, the electric repulsion is the greatest at those points at which it is accumulated in the largest quantity; and it is natural thence to conclude that

10*

this

this is a general property appertaining to every variety of form: but it is difficult to demonstrate it on principles purely analytical. Laplace, however, has demonstrated it synthetically from which it results that the variable pressure at the surface of electrified bodies is proportional to the square of the thickness; and, consequently, where this pressure exceeds that which is opposed to it by the air, the latter must yield, and the fluid will escape as at an opening, which is exactly the fact that takes place at the extremity of points and the sharp edges of angular bodies. The principles employed as the basis of this theory will apply equally to an isolated body, or to any number of them exposed to each other's influence: for, in order that all the bodies may remain in a permanent state of electricity, it is necessary, and it will be sufficient, that the resultant of the actions of the fluid-lamina on any point assumed in the interior of one of the bodies may be equal to zero. The application of this principle will furnish, in every case, as many equations as there are conducting masses; which equations will serve to determine the variable thickness of the electric lamina in the different bodies.

On a remarkable Modification experienced by the Rays of Light, in their Passage through certain Diaphanous Bodies; and on some other new optical Phænomena. By M. ARAGO. These experiments, and the conclusion drawn from them, were made more than eight years ago; since which time they have been the subject of many interesting articles and of numerous experiments both in this country and in France, and are too well known to require any farther notice in this place.

On the new Relations which exist between the Reflection and the Polarization of Light by crystallized Bodies. By M. BIOT. -The same remark applies to this article as to the preceding: to which we may also add that its length defies the condensation of it into any intelligible form, within the limits to which it is necessary for us to confine our present report.

(Part II.) PHYSICS AND CHEMISTRY.

M. CUVIER'S analysis of the labours of this class, during the year 1811, is no doubt drawn up with every degree of attention and skill; yet it is not very interesting, in consequence of the materials which compose, it being in themselves rather unimportant, and appearing still more so from the length of time which has elapsed since they were brought before the class. In the department of Natural Philosophy and Chemistry, after having mentioned the discovery made by Prof. Leslie, of augmenting the effect of evaporation in producing artificial cold, by placing under the receivers of an APP. REV. VOL. LXXXIII.

Mm

air

air-pump a body peculiarly disposed to admit the vapour that is generated, M. CUVIER notices some experiments that have been made on the same subject by MM. Clement and Desormes, especially with a view to ascertain whether this process be capable of being rendered useful in an economical point of view. Some improvements also in the art of distillation, made by M. Adam of Montpelier, are likewise reported. They essentially consist in heating the fluid employed in one stage of the process, by the vapour that has been formed in a previous stage; a mode which, we believe, has been long known to manufacturers in this country.-We have next an account of the experiments of Count Rumford on the question respecting the nature of light, whether it be a substance which emanates from the luminous body, or whether it be only a certain kind of motion, impressed on some subtile fluid which is diffused through space. He decided in favour of the latter opinion; because he found that the intensity of light, as emitted from a body during combustion, bore no proportion to the quantity of matter actually consumed, but rather to the intensity with which the combustion was carried on. The experiments have been some time before the public; and, though they do not prove the point intended by them, they are marked by that ingenuity which was so characteristic of the author.

Next occurs the mention of some suggestions by M. Deyeux on the cultivation of the Beet; of M. Deslonchamps on the cultivation of the Opium-poppy in France; and of M. Chevreul on Indigo. We have likewise an account of some experiments of M. Dulong on the question whether insoluble salts are capable of exchanging their principles with certain soluble salts, and which lead him to this conclusion; that all the insoluble salts are decomposed by the carbonates of potash and soda, but that the complete mutual exchange of their principles does not take place in any instance; and reciprocally that all the soluble salts, the acid of which can form an insoluble salt with the base of the insoluble carbonates, are decomposed by them until the decomposition has arrived at a certain limit which we cannot pass: so that, in identical circumstances, combinations are produced absolutely opposite to each other.' The reporter then notices the process by which M. Gay-Lussac has obtained the Prussic acid in a state of very high concentration; and the observations of M. Oberkampf on the preparations of Gold.

We find nothing very remarkable under the heads of Meteorology, Mineralogy, and Zoology: but in Vegetable Physiology we have a longer detail, first of some experiments,

by

by M. Palisot de Beauvois on the progress of the Sap, and on the mode of fecundation of the Mosses; and afterward of MM. Mirbel and Richard on the interior structure of some kinds of Seeds, in which the use of the cotyledons is discussed, and the merit of the system is considered which takes its fundamental division from the number of these organs. This circumstance seems to have given rise to a warm controversy between these botanists on the nature of the parts of certain plants, in which we do not feel ourselves disposed to

enter.

On the subject of Anatomy and Physiology, the experiments and observations of M. LE GALLOIS hold a distinguished rank: but, as they have been for some time well known in this country through the medium of different journals, we shall not now attempt any detail respecting them; only observing that, although they are ingenious and important, we do not think that they lead to all the conclusions which the author has deduced from them. On the topics of Medicine and Surgery, we observe nothing that will be interesting to our readers.

After the History come two éloges by M. CUVIER, one on M. Desessarts, a physician, and the other on our countryman Cavendish, who was one of the foreign members of the Institute. M. Desessarts was the son of a surgeon, and was born in the department of the Aube, in 1729. He lost his parents early in life, but was brought up by an uncle, who was a professor in the College of Beauvais; and he was placed under the care of the Jesuits, who were very anxious to enlist him into their order. He fixed, however, on the profession of medicine, which he pursued with ardour during the remainder of his life, devoting to it almost the whole of his attention. The eulogist says that no one was more a physician, or a physician of more devotedness; medicine being to him a second religion, the duties of which have filled up his long life. Thinking neither of glory nor of fortune, and incapable of jealousy, even to his latest days, he studied and collected with the candour of a young man all that had any connection with his art; and at the age of 82 years he supplied our sittings with memoirs and extended reports on any medical works that appeared.' The events of his life, however, are not particularly interesting; nor do his works, which seem to have been chiefly professional, require any special notice. With respect to the account of Mr. Cavendish, we shall not consider it as necessary to enter into any detail on a subject which must be well known to all our scientific readers: but we may observe that M. CUVIER, as indeed is always the case, is not backward to M m 2 acknow