plate is marked by a graduated circle screwed upon the side of the table. On the brass table is placed a movable flat plate of brass, divided into rhumbs and degrees, and furnished with a magnetic needle, with an agate cap traversing on a brass or steel paint. The needle can be changed according to the nature of the circumstances, a very light, and strongly magnetized one being used in delicate experiments. The compass, or plate, carrying the needle, being movable, its distance from the bar resting on the movable plate, can be varied at pleasure. The centre of the hinges is one tenth of an inch above the level of the table; the magnetized needle stands at the same elevation; and the bars in use being one-fourth of an inch in diameter, are sunk in the groove of the movable plate to such depth, that their axis, or centre, precisely corresponds with the centre of the hinges; hence the middle of the extremity of each bar is at the same elevation, and at the same distance from the needle, in every position of the movable limb. To give firmness to the instrument, in making experiments, the table is fixed by the feet to a mass of lead, of seven or eight pounds weight. By means of this plate of lead, which has a screw at each corner, the whole apparatus is readily put into a horizontal position. With this apparatus, Mr Scoresby made a series of experiments, which are fully detailed in the Transactions of the Royal Society of Edinburgh, vol. IX. p. 243, to which we beg leave to refer.

ings, and a description of a 25 feet reflecting telescope, constructed by Mr John Ramage of Aberdeen. Excepting those of the celebrated Sir W. Herschell, this, we believe, is the largest telescope ever constructed, and does honour to Scotland, as well as its ingenious author. The speculum is 25 feet in focal length, and 15 inches in diameter. The method of observing is by the front view; the power is from 50 to 1500; and the mechanism by which the observer and the instrument are moved, is so simple and well contrived, that it can be managed and directed to any point of the heavens as readily as a three feet achromatic telescope.

On the 2d of April, there was read to the Society a letter from Sir David Milne, Bart., to Professor Russel, giving an account of the method of fishing for large corals in the Island of Bermuda. They are found round the island in large abundance, in about three feet water at low tide; and are principally attached to the edge of the coral reefs, where the water deepens suddenly to 10 or 18 feet. They are fixed to the reef by a kind of stalk, and seem of all sizes, from two inches to several feet in diameter, growing in clusters like mushrooms. When first taken out of the water, they are of a light brown or snuff colour; but after a few weeks exposure to the sun, they become perfectly white.

THE Royal Institute of France, as our readers may perhaps know, consists of four branches, called Academies; the Academy of Sciences, the Academy of Inscriptions and Belles Lettres, the Academy of Fine Arts, and the French Academy, each of which strictly confines itself to its own appropriate department of knowledge or of art. Of these different branches, however, by far the most distinguished, is the Academy of Sciences, which reckons among its members, the most eminent scientific characters of the age; and to the proceedings of which alone, the present abstract will, therefore, be entirely restricted. This determination has been rendered imperative on our part, both by the narrow limits to which we are confined, and the comparatively unimportant and uninteresting character of the proceedings of the other three academies, which, from the decided preference given to science, both during the revolution, and subsequently under the imperial government, have lost much of that reputation, (particularly the Academy of Inscriptions and Belles Lettres,) which they possessed under the ancient regime.

The Academy of Sciences commenced its sittings for the year 1820, on the 3d of January, when M. Boué read a Memoir, entitled, "A Geological Essay on Scotland," which he has since published, in an enlarged form, thereby superseding the necessity of any particular notice in this place. On the 17th, M. Biot read a paper, entitled, "On a New Physical Property which Plates of Glass acquire, when they perform Longitudinal Vibra

tions." The property of which M. Biot speaks, is the power which glass acquires, while in a state of vibration to depolarize the light which traverses it. Having prepared a larger faisceau of polarized light, he received it on a plate of black glass, so placed as to occasion no reflection, and the actual state of which he had examined before interposing it to the path of the light. Some traces were now discovered, of colours corresponding to the tints of the primary rings of Newton's table, and bearing an evident analogy to those presented by longitudinal pieces of glass, which have been powerfully heated, and then rapidly cooled. There was this peculiarity, however, that these traces were most sensible towards the middle of the piece of glass, whether viewed in front, or laterally, and that they rapidly diminished towards the two sides of this middle part, so as to disappear entirely at the extremities. But when the plate of glass was interposed in the path of the ray, so that the ray might pass directly through its thickness, which was about seven millimétres, (.27559 inches,) a slight change was with difficulty perceived, in the languid reflection which took place on the blackened glass, prepared to absorb the polarized ray; but if one-half of the plate of glass, taken by the middle, was rubbed with a moistened cloth, so as to excite longitudinal vibrations, while the other half was placed in the path of the faisceau of polarized light, at each time a sound was produced, a brilliant flash of white light shone on the surface of the absorbent glass, which proves that a change had taken place in the direc

tion of the polarization; and the more the sound (its tone remaining the same) became full and intense, the brighter was the light thus perceived, while the moment it ceased, the absorbent glass resumed its original state, and the polarization its primitive direction. If, instead of transmitting the polarized faisceau across the thickness of the plate, which was seven millimétres, it was directed across its breadth, which was 30, (1.18110 inches,) immediately delicate lines of colour, analogous to the first order of rings, appeared in the direction of the length of the plate, modifying the primitive coloured striæ, and presenting, not only the bluish white of the first order, but descending even to the orange. M. Biot concluded the detail of these curious experiments, by some remarks on the ratio of the distribution of the light elicited by these vibratory motions in the particles of the plates of glass, and by a comparison of the results with some previous experiments by MM. Savart and Chladny.

At the same sitting, M. Dumeril, in the name of a committee, made a report of a case in practical medicine, which had been communicated to the Academy by M. Chomel. A young woman, after having experienced several attacks of hysteria, was seized with a periodical cough, which commenced every day about two o'clock, and continued with extraordinary violence for seven or eight hours. This periodical access of coughing had been transformed into real attacks of hysteria, and this conversion, provoked, or produced, by the administration of extract of belladona, (deadly nightshade,) was, in this particular case, the more fortunate, as the attacks of hysteria yielded easily to the administration of quinquina (Peruvian bark).

The proceedings of the Academy, in February, do not call for any par

ticular notice. At the sitting of the 6th of March, M. Cauchy made a report on a Note of M. Lepely, relative to the summation of descending progressions. This Note contains the curious proposition, which, however, may be demonstrated by a simple comparison of triangles, that if, in a trapezium having three sides equal to one another, and smaller than the fourth, the two sides not parallel be produced till they meet, the lengths comprised under these two sides, between the point where they meet, and the base of the trapezium, will be numerically equal to the sum of the descending geometrical progression, which shall have for its ratio, the relation between the two parallel sides; and for its term, the smallest of these sides.

On the 13th, M. de Humboldt read a most ingenious memoir, "On the Nocturnal Increase in the Intensity of Sound." This phenomenon has been remarked from the remotest antiquity. Aristotle speaks of it in his Problems, (Sect. XI. quæst. 5 and 23,) and Plutarch in his Dialogues, (Sympos. Lib. VIII. cap. 3. vol. II. p. 720, Franck. Edit. 1620,) and numerous attempts have at different times been made, to give a satisfactory solution of a fact, which every one must have observed. Prior to that proposed in the memoir of this celebrated traveller, we are not aware of any that deserve the name of scientific, or serve, even in an imperfect degree, to explain and connect the numerous facts which have been observed and recorded. In this paper, the ingenious author considers only the increase of intensity in a tranquil state of the atmosphere, there being no difficulty as to that produced by the wind during the night, and which is modified by the relation subsisting between the direction of the wind and that of the sonorous ray. Under the same zone, for example, between the tropics, the nocturnal increase of the

intensity of sound appeared to the author greater in the plains than on the back of the Andes, at the height of 3000 mètres (9843 feet) above the level of the ocean, and more consider able in low regions in the midst of continents than in the open sea. In these differences between the higher and lower regions of equinoctial America, the relations of intensity are considered under the same barometrical pressure, the object of the author being not to compare the absolute intensity at different heights, but the difference between the nocturnal and diurnal intensity on the plateaux and on the plains. The sound of the Grand Cataracts of the Oronoco, heard at the distance of more than a league, in the plain which surrounds the mission of Atures, creates a belief that one is in the vicinity of a coast studded with reefs and breakers, is three times louder in the night than during the day, and gives an inexpressible charm to these solitary regions. What can be the cause of this increase of intensity in a desert where nothing exists to disturb 19 the silence of nature? This, the author shews, cannot be owing to the diminished temperature during the night, which, instead of augmenting, rather retards the rapidity with which sound is propagated. The same effect is produced by a current of wind opposed to the direction of the sound, and by the dilatation of the air, by which the density, and consequently the elasticity are diminished. Nor, in regions uninhabited by man, can this remarkable phenomenon be accounted for by the cessation of the humming of insects,

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the chaunting of birds, or the rustling of leaves; for in the forests which border on the Oronoco, the air is constantly filled with innumerable multitudes of mosquitos; the humming of insects is much stronger during the night than during the day; and the breeze, if felt at all, does not blow till after sun-set. The author thinks that the presence of the sun acts on the propagation and intensity of sound, by the obstacles opposed by currents of air of different density, and the partial undulations of the atmosphere, caused by the unequal heating of different parts of the soil. In a tranquil state of the air, whether it be dry, or charged with humidity, the sonorous wave is propagated without difficulty but when the atmosphere is traversed in all directions, by small currents of warmer air, the sonorous wave is divided into two parts, one of which returns upon the other, and retards the propagation of sound; in short, the cause is to be sought for in the want of homogeneity in the elastic medium. In order to give a precise idea of these currents of heated air which rise during the day from a soil unequally acted on by the sun's rays, the author relates several experiments which he made under the tropics. In the Slanos or Steppes of Venezuela, he found the sand, at two o'clock in the day, at 52.5°, and sometimes even at 60° of the Centigrade thermometer, (126.5° and 140° Fahr). The temperature of the air in the shade of a Bombax, was 36.2° (97.16° F.); in the sun, at 18 inches above the ground, 42.8° (1099 F.). In the night, the temperature of

VOL. XIV. PART II.

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the sand was only 28° (82.5° F.); it had lost more than 24° (43.2° F.) Near the cataracts of the Oronoco, the soil being covered with a rich vegetation, is seldom heated, during the day, beyond 30°, (86° F.,) the air being 26° (79° F.), while the immense masses of surrounding granite, are, at the same time, heated as high as 48° (118.4° F.). If the cause of the nocturnal increase of sound, here pointed out, be true, it need surprise no one, that under the torrid zone, this increase should be greater in the interior of the continent than in the open sea; in the plains, than on the back of the Cordilleras. The surface of the sea is uniformly heated, and never above 29° C.; while the surface of the continents, unequally coloured, and composed of materials which radiate differently, acquires, near the equator, temperatures which vary from 30° C. to 52° C. Under the tropics, the earth is generally, during the night, warmer than the air; in the temperate zone, during calm and serene nights, it becomes 4° or 5° C. colder. In a word, the phenomenon depends upon that want of homogeneity in the vertical columns of the atmosphere, which, according to M. Arago, is also the true cause of the scintillation, more or less vivid, of the

stars.

At the same sitting, M. Duméril read a report, in name of the Committee appointed to examine the Memoir, presented to the Academy, by M. Devèze, and in which he discusses the important question, Whether the yellow fever be contagious? We are induced to notice this Memoir, because many of the opinions entertained by the author, on the subject of contagion and infection, differ entirely from those of which we have already had occasion to speak, in submitting to our readers, a condensed abstract of the facts

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and reasonings in Dr Ferguson's able paper, read to the Royal Society of Edinburgh, (and since published in vol. IX. of their Transactions) on the subject of Miesma. M. Devèze thinks that the yellow fever is not contagious, and that its developement and propogation are the result of infection. In fection, according to this author, is a morbific mode by which a centre of putrefaction gives to an individual, subjected to its influence, the pre-disposition to contract a disease of a particular description, or, at least, occasions the determination of that disease, when the individual has been already pre-disposed to contract it. The constant characteristics of infectious diseases are, that they originate in all places under the influence of a centre of putrefaction, and never anywhere else; that a great number of persons may be attacked by them at the same moment, without any previous communication between them, &c. tagion, on the contrary, is a mode of a disease by which an individual seized with a morbific affection communicates it to another, by means of a virus attached to a solid body, or suspended in the atmosphere. The facts upon which M. Devèze grounds his opinions are these: 1. In all countries where the yellow fever habitually prevails, there are places where it is never developed, except in the case of persons who have imported the germ of disease from the focus of infection: 2. Under temperate climates, the malady never spreads in the plains, and the elevated quarters of cities are often exempt from this scourge, when it ravages those parts which are low and humid: 3. In well regulated hospitals, the yellow fever never shews itself, except on those individuals who were affected with it when they entered: 4. Eighteen individuals died at Alcala de los Panderos, of the yellow fever, which they had contracted at Seville, while no inhabi