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bark of the root, is carried up by the alburnum, or white wood of the root, the trunk, and the branches; that it passes through what he calls the central vessels into the succulent part of the annual shoot, the leaf-stalk, and the leaf; and that it thence returns to the bark through the returning vessels of the leaf-stalk. The principal object of the present paper is to point out the causes of the descent of the sap through the bark, and the consequent formation of wood.

The causes to which he ascribes this descent are: 1. Gravitation; 2. Motion communicated by winds or other agents; and 3. Capillary attraction, and perhaps some peculiar circumstances in the conformation of the vessels themselves, which renders them better calculated to carry fluids in one direction than in another.

Before he proceeds upon the experiments from which he has deduced these conclusions, he premises a few observations on the functions of the leaf, from which all the descending fluids in the tree appear to be derived. He describes an experiment he made on a leaf of a vine, in which its lower surface being placed in contact with a clean piece of plate glass, this glass was soon found to be covered with a strong dew, which had evidently exhaled from the leaf; and at the end of half an hour so much water was found to have been discharged from the leaf, that it ran from the glass when it was held obliquely. The position of the leaf being then inverted, and its upper surface being brought in contact with the glass, not the slightest portion of moisture appeared, although the leaf was for some time exposed to the full influence of the meridian sun. Hence it is inferred, that the vessels intended for perspiration are confined to the under surface of the leaf, and that these, like the cutaneous lymphatics of the animal œconomy, are also capable of absorbing moisture when the plant is in a state to require it; whereas the upper surface seems chiefly formed for absorbing light; and if anything exhale from it, it is probably vital air, or some other permanently clastic fluid.

Reverting now to the principal object of his paper, the author describes an experiment on a shoot of a vine, which he bent downwards nearly in a perpendicular direction. After it had grown some time in this position, and acquired a ligneous texture, he stripped the bark from a part of it, and thus cut off all communication through the bark between the shoot and the parent stem. Former experiments have shown, that had this shoot grown in its erect position, the lip of the bark above the wound would have shown an accumulation of fresh wood and bark; but in this instance the contrary was found to be the case; the lip next to the stem, which by its position was now uppermost, gave evident signs of this accumulation. This is ascribed to the gravitation of the sap, from the curvature of the shoot down to the lip. The result of this experiment scems to point out one of the causes why perpendicular shoots grow with much greater vigour than those which are inclined or horizontal, they having probably a more perfect and rapid circulation.

The effect of motion on the circulation of the sap was deduced

found in fruits, in which it is modified by sugar and acids; that he has found it in great abundance in the juice of sloes, and that a friend of his had discovered its presence even in port wine. It also appears that it may exist in a state of combination in different substances, in which its presence cannot be made evident by the common means of solutions of gelatine; and that in these cases, in order to detect its existence, it may be necessary to have recourse to the action of diluted acids.

General Observations.-After a few strictures concerning a conjecture of Mr. Proust, that there are different species of the tanning principle possessed of different properties, and different powers of acting upon re-agents, from which our author thinks himself authorized to dissent, he draws the general conclusion,-that in all the different astringent infusions the tanning principle is found possessed of the same general properties and powers of combination. In all instances it is capable of entering into union with the acids, alkalies, and earths; and of forming insoluble compounds with gelatine and with skin. That in the processes of tanning, if the astringent infusion contain extractive and colouring matter, these as well as tannin enter into chemical combination with the skin; but that in no case is there any reason to believe that gallic acid is absorbed in this process. That hence the different qualities of leather made with the same kind of skin, seem to depend very much upon the different quantities of extractive and colouring matter it contains; the leather prepared by means of infusions of galls being generally found harder, and more liable to crack than that obtained from the infusions of bark.

When skins are slowly tanned in weak solutions of the barks, or of extract of catechu, it combines with a considerable proportion of extractive matter, whereby it is rendered perfectly insoluble in water, and yet soft and very strong. The inference, perhaps the most essential, deduced from this inquiry is, that of all the astringent substances as yet examined, the extracts of catechu are those that contain the largest proportion of tannin, half a pound of this extract being found to produce the same effect in tanning as from four to five pounds of common oak bark.

How material this must be in a country where oak timber is not an object of trivial importance, need not be here insisted upon.-The paper closes with a table, in which oak bark being taken as the standard of comparison as to its quantity of tannin, the different astringent substances are arranged in the order of their powers.

In

Account of some Experiments on the Descent of the Sap in Trees. a Letter from Thomas Andrew Knight, Esq. to the Right Hon. Sir Joseph Banks, Bart. K.B. P.R.S. Read April 21, 1803. [Phil. Trans. 1803, p. 277.]

In a former paper Mr. Knight related some experiments on trees, from which he inferred that their sap, having been absorbed by the

bark of the root, is carried up by the alburnum, or white wood of the root, the trunk, and the branches; that it passes through what he calls the central vessels into the succulent part of the annual shoot, the leaf-stalk, and the leaf; and that it thence returns to the bark through the returning vessels of the leaf-stalk. The principal object of the present paper is to point out the causes of the descent of the sap through the bark, and the consequent formation of wood.

The causes to which he ascribes this descent are: 1. Gravitation ; 2. Motion communicated by winds or other agents; and 3. Capillary attraction, and perhaps some peculiar circumstances in the conformation of the vessels themselves, which renders them better calculated to carry fluids in one direction than in another.

Before he proceeds upon the experiments from which he has deduced these conclusions, he premises a few observations on the functions of the leaf, from which all the descending fluids in the tree appear to be derived. He describes an experiment he made on a leaf of a vine, in which its lower surface being placed in contact with a clean piece of plate glass, this glass was soon found to be covered with a strong dew, which had evidently exhaled from the leaf; and at the end of half an hour so much water was found to have been discharged from the leaf, that it ran from the glass when it was held obliquely. The position of the leaf being then inverted, and its upper surface being brought in contact with the glass, not the slightest portion of moisture appeared, although the leaf was for some time exposed to the full influence of the meridian sun. Hence it is inferred, that the vessels intended for perspiration are confined to the under surface of the leaf, and that these, like the cutaneous lymphatics of the animal œconomy, are also capable of absorbing moisture when the plant is in a state to require it; whereas the upper surface seems chiefly formed for absorbing light; and if anything exhale from it, it is probably vital air, or some other permanently clastic fluid.

Reverting now to the principal object of his paper, the author describes an experiment on a shoot of a vine, which he bent downwards nearly in a perpendicular direction. After it had grown some time in this position, and acquired a ligneous texture, he stripped the bark from a part of it, and thus cut off all communication through the bark between the shoot and the parent stem. Former experiments have shown, that had this shoot grown in its erect position, the lip of the bark above the wound would have shown an accumulation of fresh wood and bark; but in this instance the contrary was found to be the case; the lip next to the stem, which by its position was now uppermost, gave evident signs of this accumulation. This is ascribed to the gravitation of the sap, from the curvature of the shoot down to the lip. The result of this experiment scems to point out one of the causes why perpendicular shoots grow with much greater vigour than those which are inclined or horizontal, they having probably a more perfect and rapid circulation.

The effect of motion on the circulation of the sap was deduced

Each of these hypotheses having been carefully investigated, it is found that all except that of a rotatory motion of the small star round the large one, or of their joint motions round a common centre of gravity, offer difficulties which cannot be surmounted. Adopting, therefore, this last-mentioned hypothesis as the true one, our author proceeds to a more detailed examination of the several angles of position he has taken in the course of his observations; and having also determined those angles by calculation from the annual rate of 56′ 18", deduced from the total change in the whole period, he finds the agreement so obvious as hardly to admit of a doubt of this being the true mode of accounting for these variations. He has, moreover, the satisfaction of being able to quote an observation of Dr. Bradley, made in the year 1759, which he lately obtained from Dr. Maskelyne; according to which, the two stars of a Geminorum were in that year seen in an angular position, exactly corresponding with the situation they ought to have been in, according to the rate here assigned for their rotatory motion: so that the time of a periodical revolution may now be calculated from an arch of 45° 30', which has been described in forty-three years and a half.

Thus, from the great regularity of this motion, he now thinks himself authorized to conclude, that the orbit in which the small star moves round the large one, or perhaps the orbits in which they both move round their common centre of gravity, are nearly circular, and at right angles to the line in which we see them; and that the time of a whole apparent revolution will be about 342 years 10 months.

We shall not presume to enter here upon any detail of the investigations respecting the five other double stars mentioned in this paper, any further than to record the general results deduced from them.

In y Leonis the plane of the orbit of the small star is found not to be at right angles with the line of vision, the distances having varied considerably since the commencement of the observations, and these different distances affording the elements of an ellipsis which will explain the appearances, although the orbit be in fact, or nearly, circular. The periodical time of this revolution is calculated at about 1673 years.

As to & Bootis, the changes observed during twenty-two years indicate that one of the periodical revolutions cannot take up much less than 1681 years; but as the figure and situation of the orbit cannot as yet be accurately determined, some uncertainty still remains even concerning this period.

The observations on Herculis afforded a phænomenon hitherto unknown in astronomy; namely, an occultation of one star by another. Whether this be owing to solar parallax, to proper motion, or to the motion of one of the stars in an orbit whose plane is nearly coincident with the visual ray, is not as yet determined; nor is any periodical time hitherto assigned to it.

The periodical time of Serpentis is calculated at 375 years, and that of y Virginis at 705 years. Their distances have not varied for

many years back; whence it may be inferred that the planes of their orbits are really or nearly at right angles with the visual ray.

Dr. Herschel being aware that the observations he brings forward in this paper are of a nature so delicate and minute as to afford opportunities for cavil, has been at considerable pains to point out the principal circumstances that contribute to the perfection of telescopes and micrometers, and the precautions to be used as to the state of the atmosphere. Those ought, he thinks, to be particularly attended to by accurate observers.

An Account of the Measurement of an Arc of the Meridian, extending from Dunnose, in the Isle of Wight, Latitude 50° 37' 8", to Clifton, in Yorkshire, Latitude 53° 27' 31", in course of the Operations carried on for the Trigonometrical Survey of England, in the Years 1800, 1801, and 1802. By Major William Mudge, of the Royal Artillery, F.R.S. Read June 23, 1803. [Phil. Trans. 1803, p. 383.]

In this paper we are presented with a further continuation of the several accounts given, ever since the year 1785, of the trigonometrical surveys carried on over various parts of the kingdom. Having now proceeded a great way in these surveys, Major Mudge thought it high time to attempt the measurement of a considerable arc of the meridian in our latitudes. He first assigns his reasons for preferring the meridian he has here adopted, which depend chiefly on the nature of the country being less hilly and liable to less obstruction than any other tract of the length of this arc in the island. He fixed on Dunnose, in latitude 50° 37' 8", for the southern extremity, and on Clifton, a small village in the vicinity of Doncaster, latitude 53° 27′ 31′′, for the northern termination of this arc: and near the latter place he found a convenient plain, viz. Misterton Carr, for the measurement of a base of verification.

As the accuracy of the zenith observations would be most essential towards the perfection of this measurement, a new zenith sector was constructed for the purpose by Mr. Ramsden, and finished by Mr. Berge, the excellence of which is here attested by its being called the first instrument of its kind. Its merits consist chiefly in the means of uniting the sectorial tube to its axis, so as to insure the permanency of the length of its radius when erected for observation; in a more accurate method of adjusting the instrument vertically; an easy way of placing the face of its arch in the plane of the meridian; and a contrivance by which the plumb-line can be brought precisely over the point marking the centre of the circle, of which the divided arch of the sector should be a part.

Having given a minute description of this instrument, and of the preparatory operations for the series of observations to be made with it, such as the construction of a proper observatory, and other auxiliary requisites, the author proceeds to give us, in different tables,

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