the bark.

For this purpose, circular incisions were made round a number of young healthy trees, and the bark removed for the space of about half an inch, or more, of the whole circumference. This, it was found, by no means impeded the growth of the upper part of the tree; but, on the other hand, the part of the stem below the incision scarcely grew at all, and in time even seemed to wither. From the whole of this investigation it seems probable, that the current of sap which adds the annual layers of wood to the stem, so far from ascending, actually descends from the young branches and leaves through the bark. The branches and leaves which supply this fluid became hence the next objects of the inquiry.

The conjecture just now mentioned was here confirmed by the circumstance, that when a branch or leaf was left between two circular incisions, it continued to receive its nourishment as usual; and the bark under it gave evident marks of increasing vegetation, while that above was not only stationary, but seemed even to decay.

It became now necessary to investigate by what channels leaves receive their nourishment. Some annual shoots were cut from trees, and placed in a coloured infusion. Although this fluid, it was observed, certainly rose into the leaves, yet neither the bark nor the medulla was sensibly tinged by it; but in the centre of the stalks of the leaves were found several bundles of tubes which had been manifestly coloured, and must hence have been the channels of communication. These tubes were surrounded by others, which, being traced downwards, were found to enter the inner bark, and by no means to communicate with the tubes of the wood: these being colourless, it may reasonably be concluded that they convey a different fluid from that which ascends into the leaf.

To the former, or internal tubes, which had not yet been distinguished by any name, the author thinks fit to assign the appellation of Central Vessels. He then mentions certain spiral tubes which are everywhere appendent to these vessels, and seem to proceed from the sides of the medulla to the leaf-stalk. Particular attention is then paid to the action of the medulla. By extracting parts of it out of the stems of trees, so as completely to interrupt its continuity, it was proved beyond a doubt that it is nowise necessary for the progression of the sap, the tree growing equally, whether this marrow be or be not continued.

The next set of experiments relates to the fructification: and here central tubes were likewise found in the fruit-stalks, which, there is reason to think, are the nourishing ducts of those productions. Many curious circumstances are here mentioned concerning the internal organization and mode of nutrition of certain fruits, such as apples and pears, for which, as well as for several observations on the error of those who have ascribed the ascent of the sap to capillary tubes, or to the sole agency of heat, we must refer to the paper, in order to hasten to the part in which the author points out an agent to which he thinks the mechanical propelling force required may be reasonably ascribed.

In all kinds of wood, he says, there are two sorts of grain,-the false or bastard, and the true or silver grain. The former consists of the concentric circles which mark the annual increase of the tree; and the latter is composed of thin laminæ, diverging in every direction from the medulla to the bark, with different degrees of adhesion to each other at different seasons, and lying between and pressing on the sap-vessels of the alburnum.

If these laminæ are expansible under various changes of temperature, or from any other cause arising from the powers of vegetable life, our author conceives that they are as well placed as is possible to propel the sap to the extremities of the branches. That they are affected by the changes of temperature in the air is proved by the effects of these changes on them even after the tree is dead, as in the instance of boards, which warp more or less, according to the direction of this grain: and other instances are given of the effects of solar heat on different parts of plants, which materially favour this assertion.

The general conclusions derived from these experiments are, That the tubes of the alburnum, acted upon by the agency of the silver grain, are in fact the channels which, extending from the extremities of the roots to the points of the annual shoots, convey the nutricious juices to the base of the buds, and in the soft and succulent part of the annual shoot, where the alburnum with the silver grain ceases to act, and where commences the action of the central vessels, with their appendages the spiral tubes;-that having through these reached the end of the leaves, the sap undergoes a change, perhaps from the action of the atmosphere, and is then brought back again through the external vessels of the leaf-stalks to the bark, which conveys it to every part of the tree, and ultimately contributes to its growth.

In speaking of the use of the medulla, the author assigns his reasons for considering it as a reservoir of moisture, which it occasionally imparts to the leaves and fruit through the central vessels, and which these organs must often stand in need of, as they cannot, like animals, resort to the brook or shade. The heart or coloured wood of the trees he considers as the bones in the animal œconomy, being intended to support them against the effects of winds and other destructive agents; and, accordingly, it is not found in roots or tender shoots, but is only formed when the vegetable has acquired a bulk which renders such a structure necessary.

Additional Observations tending to investigate the Symptoms of the variable Emission of the Light and Heat of the Sun; with Trials to set aside darkening Glasses, by transmitting the Solar Rays through Liquids; and a few Remarks to remove Objections that might be made against some of the Arguments contained in the former Paper. By William Herschel, LL.D. F.R.S. Read May 14, 1801. [Phil. Trans. 1801, p. 354.]

This may be considered as a supplement to Dr. Herschel's paper on the nature of the sun, lately read to the Society, and consists

chiefly of a continuation of his observations on the appearances of that body from the 2nd of March to the 3rd of May last.

Conceiving that there might be some advantage in getting rid of the darkening glasses in viewing the sun, he was led to substitute for them various liquors, such as spirits of wine, port wine, ink diluted with water, a solution of green vitriol with a small proportion of tincture of galls, and even plain water; which latter he found keeps off the heat so effectually, that the brightest sun may be viewed some time through it without any inconvenience.

Through diluted ink, the image of the sun appeared as white as snow; and when the liquor was still more diluted, the sun was of a purple hue, while the objects on its surface continued as distinct as when seen through any other medium. From these observations the author infers that the continuance of the symptoms which in his former paper he considered as favourable to the copious emission of light and heat from the sun, are sufficiently verified, and that by comparing these phænomena with the corresponding mildness of the season, his arguments respecting the connexion between them and the temperature of our atmosphere acquire no small degree of probability.

Being well aware that the price of wheat which he adopted in his former paper as a criterion of the seasons is liable to some objections, the author desires here to be understood, that his intention was merely to compare the astronomical fact of the variable emission of the sun's rays with the obvious symptoms corresponding with that circumstance; leaving it to others to apply the subject to such useful œconomical purposes as may be found to have any relation to them at any rate, he cannot relinquish the hope that astronomy will ultimately supply us with the means of deriving certain prognostics of the temperature of the seasons from accurate observations on the quantity of the light we receive from the sun.

On an improved Reflecting Circle. By Joseph de Mendoza Rios, Esq. F.R.S. Read June 4, 1801. [Phil. Trans. 1801, p. 363.]

The great utility of Hadley's quadrant in practical astronomy, and particularly in navigation, has given rise to several improvements of that valuable instrument, of which some account is premised in the present paper. The first of these is due to the celebrated Tobias Meyer, who, by completing the limb of the sextant into a whole circle, and adding an horizon index, enabled us to repeat the observations, so as to ascertain the double, triple, and even a greater multiple of the angles; by which means the errors of division or eccentricity in the instrument can be reduced in the inverse ratio of the repetition of the observations, so as to arrive at any degree of approximation that may be required.

Some imperfection still remaining as to the manner of rendering the glasses parallel, so as to produce the exact coincidence of the images, the Chevalier de Borda contrived a method of rendering this exact parallelism of less consequence, by substituting the immediate

observation of the angular distance of the two objects to that of the coincidence of their images in one field. In his instrument the telescope is fixed at such a distance from the centre that the rays of light may arrive at the centre-glass both from the right and the left: double distances and cross observations are thus easily obtained, which essentially correct any imperfection in the construction of the instrument.

The peculiar advantages of these improvements being chiefly to afford the means of multiplying the observations of the distance required, Mr. Mendoza has directed his attention to some further improvements, which he thought might be deduced from the same principle. He accordingly favours us with an account of his new reflecting circle, of which a distinct idea can only be obtained by an inspection of the three accurate delineations which accompany his paper.

One of the additions is a compound handle, which facilitates the holding the instrument with the same ease in every direction. But the chief improvement appears to be a divided circle, moving round the centre, within, and close to the graduated limb, and capable of being alternately attached to each of the indexes. This the author calls the Flying Nonius; and shows how in every direction the two divisions may be made to exhibit the number of degrees on the limb, and of the minutes and seconds on the flying nonius. The manner in particular of making the crossed observations, by connecting the limb and the nonius alternately with the centre and horizon indexes, is here fully explained. And lastly, a small graduated semicircle is added to the horizon index, the use of which is to prepare the instrument previous to an observation, so as to facilitate the operation of bringing the images to coincide in the field of the telescope.

Observations and Experiments upon Dr. James's Powder; with a Method of preparing, in the humid Way, a similar Substance. By Richard Chenevix, Esq. F.R.S. M.R.I.A. Read June 4, 1801. [Phil. Trans. 1801, p. 375.]

From the experiments of Dr. Pearson on the nature of Dr. James's powder, published in the 81st volume of the Philosophical Transactions, our author infers that the mode in which it is prepared is far from being the best that the present improved state of chemical knowledge might afford; the use of fire in delicate processes, whether analytical or synthetical, being in general thought inferior to those performed in the humid way.

This powder, we are told, is prepared by mixing equal quantities of bone shavings (or phosphate of lime) and crude antimony, and calcining them together in an intense heat.

Here it is observed, that the portion of oxide of antimony, which is not volatilized in the process, becomes in a great measure insoluble in all acids. The humid process which Mr. Chenevix recommends as preferable to the above, consists in dissolving together or separately,

in the least possible portion of muriatic acid, equal parts of the white oxide of antimony and phosphate of lime; after which, pouring this solution gradually into distilled water previously alkalizated by a sufficient quantity of ammonia, a white and abundant precipitate will be produced, which, being well washed and dried, is the substitute he proposes for James's powder. A few observations are added on the theory of this combination; as also an assertion, that this powder, administered as a medicine, perfectly agreed in its general effects with James's powder, and the pulvis antimonialis, often prescribed in lieu of it, with this advantage, that being more mild, it may be given in larger doses, without producing the nausea or other stimulating symptoms that usually attend it.

Case of a young Gentleman, who recovered his Sight when seven Years of Age, after having been deprived of it by Cataracts, before he was a Year old; with Remarks. By Mr. James Ware, Surgeon. Communicated by Maxwell Garthshore, M.D. F.R.S. Read June 11, 1801. [Phil. Trans. 1801, p. 382.]

The subject of this case was the son of a clergyman in Somersetshire, who in his early infancy had every appearance of being a healthy, perfect child; but, when about a year old, was accidentally observed to be deprived of sight. A surgeon in the country pronounced that he had a complete cataract in each eye; and Mr. Ware, on being consulted, did not hesitate to decide that the only cure would be the removal of the opaque crystalline humour; but he added, that he did not think the child would be fit for the operation until he was at least thirteen or fourteen years of age. At the age of seven, however, the child's parents brought him to London, in order to enable Mr. Ware to form an opinion from his own observation. A recent case, in which this eminent operator had succeeded to restore sight to a youth about fourteen years of age, without extracting the cataract, but merely by making a large puncture in the capsule, so as to bring the opake crystalline into free contact with the aqueous and vitreous humours, having induced him to retract his opinion concerning the necessity of extracting the cataract, he proposed to perform the above operation immediately on one of the eyes of this new patient. This he effected without giving much pain; and in a few days the child described without hesitation all the objects that were set before him.

The author now draws a comparison between this case of restored sight and those described by Mr. Cheselden in the 35th volume of the Philosophical Transactions; and finding a considerable deviation in the results, he is induced to form several conclusions, which differ materially from those of his predecessors. These are briefly, That when children are born blind, in consequence of having cataracts in their eyes, they are never so totally deprived of sight as not to be able to distinguish colours :-that they have likewise some perception of distances; and that hence, when they recover their sight,