supposed to be elaborated by the leaves of the preceding summer, and, after its formation, is lodged in the alburnum until the following spring. In order to prove the truth of his hypothesis, Mr. Knight examined, at different heights from the ground, the aqueous sap as it rose in the trunk in the early part of the year; and he found that, where it was received at some distance from the root, it was of a greater specific gravity and of a sweeter taste, He examined the alburnum of wood felled at different seasons; and he found that which was felled in the winter to be of the greatest specific gravity, and to communicate more extractive matter to water. He imagines that the cotyledons of seeds, and the roots of bulbous and tuberous plants, like the alburnum of trees, contain a quantity of true sap, which has been elaborated by the leaves of the preceding summer, and which serves as a deposit for the nutriment of the following year. We cannot enter more minutely into the details of Mr. Knight's paper; his ideas are ingenious, and his arguments. plausible, though perhaps scarcely sufficient to produce irresistible conviction. We hope that he will continue to pursue his investigations into the intricate subject of vegetable physiology; since we are confident that exertions so well directed must be ultimately successful. PHILOSOPHY and ASTRONOMY. Experiments for ascertaining how far Telescopes will enable us to determine very small Angles, and to distinguish the real from the spurious Diameters of celestial and terrestrial Objects: with an App'ication of the Result of these Experiments to a Series of Oba servations on the Nature and Magnitude of Mr. Harding's lately discovered Star. By William Herschell, LL.D. F.R.S.-Small objects cannot be distinguished from each other, for instance, a small circular object from a square one,) unless the angle subtended at the eye exceeds a certain magnitude. The determination of that magnitude, when objects are viewed with the naked eye, was made by the author of the present paper in 1774: but when objects are viewed by the aid of Telescopes, new inquiries are requisite; and such are instituted and recorded in the memoir before us. The small objects employed by Dr. H. were the Heads of Pins, Globules of Sealing Wax, Silver, Pitch, Bee's-wax, &c. and the results of the several experiments are stated with the author's customary minuteness of detail. They do not, however, strike us as, very interesting, nor very important.-The memoir terminates with observations on the nature and magnitude of Mr. Harding's lately discovered star: whence it appears that this new star is to be classed with the the two that were discovered by Mr. Piazzi and Dr. Olbers, and by Dr. H. denominated Asteroids. Those readers, who recollect the definition of this new term, may understand in what peculiar circumstances the new star differs from a common planet. An Essay on the Cohesion of Fluids. By Thomas Young, M.D. For. Sec. R. S.This essay appears to us by no means sufficiently clear, precise, or full: the subject is indeed difficult, but thence necessarily arises no obstacle which prevents what is known on that subject from being exactly and simply stated. Since, however, Dr. Y. points to a period at which he shall more fully discuss it, we suppress our dissatisfaction at the obscurity in which some of the reasonings of the present memoir are involved, Some authors have asserted that the phænomena of capillary action may be referred to the cohesive attraction of the superficial particles only of the fluids concerned; and it is this principle which, if we understand him, Dr. Young adopts, expands, and endeavours to establish. Before, however, he enters on his discussions, he premises an assertion which he says is new, and consistent with theory and observation; viz. that for each combination of a solid and a fluid, there is an appropriate angle of contact between the surfaces of the fluid expo-. sed to the air, and to the solid. Water, between two plates of glass, separated by a small interval, ascends to a certainheight: mercury and other fluids ascend, the interval remaining the same, to different heights. In order, then, that the results of calculation may be compared with actual experiments, it is necessary to find the value of certain elements of the calculation such as the actual ascent of water between plates separated from each other by a determinate interval. The labours and experiments of preceding philosophers enable us to ascertain these Elements with tolerable accuracy. Dr. Y, employs some of the pages of his memoir on this subject, in the article which he names Application to the Elevation of particular fluids: but we confess that we do not exactly comprehend the connection of this article with the preceding, in which the author investigates some of the properties of the curves caused by at traction, in the simplest cases. At the conclusion of his paper, he observes: : Although the whole of this reasoning on the attraction of solids is to be considered rather as an approximation than as a strict demonstration, yet we are amply justified in concluding, that all the pheno mena of capillary action may be accurately explained and mathemati cally demonstrated from the general law of the equable tension of the surface of a fluid, together with the consideration of the angle of contact contact appropriate to every combination of a fluid with a solid.' Some anomalies, noticed by MusSCHENBROEK and others, respecting in particular the effects of tubes of considerable lengths, have not been considered but there is great reason to suppose that either the want of uniformity in the bore, or some similar inaccuracy, has been the cause of these irregularities, which have by no means been sufficiently confirmed to afford an objection to any theory. The principle, which has been laid down respecting the contractile powers of the common surface of a solid and a fluid, is confirmed by an observation which I have made on the small drops of oil which form themselves on water. There is no doubt but that this cohesion is in some measure independent of the chemical affinities of the substances concerned: tallow when solid has a very evident attraction for the water out of which it is raised; and the same attraction must operate upon an unctuous fluidto cause it to spread on water, the fluidity of the water allowing this powerful agent to exert itself with an unresisted velocity. An oil which has thus been spread is afterwards collected, by some irregularity of attraction, into thin drops, which the slightest agitation again dissipates their surface forms a very regular curve, which terminates abruptly in a surface perfectly horizontal: now it follows from the laws of hydrostatics, that the lower surface of these drops must constitute a curve, of which the extreme inclination to the horizon is to the inclination of the upper surface as the specific gravity of the oil to the difference between its specific gravity and that of water: consequently since the contractile forces are held in equilibrium by a force which is perfectly horizontal, their magnitude must be in the ratio that has been already assigned; and it may be assumed as consonant both to theory and to observation, that the contractile force of the common surface of two substances is proportional, other things being equal, to the difference of their densities. Hence, in order to explain the experiments of BOYLE on the effects of a combination of fluids in capillary tubes, or any other experiments of a similar nature, we have only to apply the law of an equable tension, of which the magnitude is determined by the difference of the attractive powers of the fluids. I shall reserve some further illustrations of this subject for a work which I have long been preparing for the press, and which I flatter myself wil contain a clear and simple explanation of the most important parts of natural philosophy. I have only thought it right, in the present Paper, to lay before the Royal Society, in the shortest possible compass, the particulars of an original investigation, tending to explain some facts, and establish some analogies, which have hitherto been obscure and unintelligible.' By An Investigation of all the Changes of the variable Star in Sobieski's Shield, from five Years Observations, exhibiting its proportional illuminated Parts; and its Irregularities of Rotation; with Conjectures respecting unenlightened heavenly Bodies. Edward Pigott, Esq.-In the first part of this paper, the author pursues the investigations begun by him some years since, relative to the changes and periods of brightness in one of the variable stars in Sobieski's shield; and the determinations pre viously viously formed by Mr. Pigott are in the present memoir revised by the aid of additional observations. Such observations were, for the space of five years, entered in a journal; and the sub stance of it, intermixed with comments and remarks, occupies the commencement of this paper. To the memoir itself we refer those who are fond of astronomical studies, since we think that a brief sketch of the remarks, reasonings, and conjectures of Mr. Pigott, must be uninteresting to the generality of readers. The usual Meteorological Journal concludes this Part of the Transactions. Part 11. for this year has just appeared. ART. VII. Elements of Self Knowlege: intended to lead Youth into an early Acquaintance with the Nature of Man, by an Anatomical Display of the Human Frame, a concise View of the mental Faculties, and an Inquiry into the genuine Nature of the Passions. Compiled, arranged, and partly written, by R. C. Dallas, Esq. 8vo. pp. 464. 10s. 6d. Boards. Murray. A MONG the number of eminent men, from whose works the author informs us that he has derived assistance in preparing these elements, the name of Cheselden is not omitted: but this general acknowlegement hardly justifies Mr. Dallas in copying verbatim so much of that anatomist's writings, as to constitute nearly the whole of the first part, which occupies about a fourth of the present volume. It often falls to our lot to toil through the numerous pages of mere compilation but we have never yet seen a mode less fatiguing, even to the mechanical powers of an author, employed in the manufacture of a book, than the extensive abstraction which we have now had occasion to notice.-In his Anatomy of the Human Body, Cheselden mentions, in the first person, a considerable number of experiments and observations made by himself on different subjects, which Mr. Dallas quotes with out modification. This will of course give him, with some readers, the credit of an experimentalist and practical observer: but this is an impression which he should have been cautious in producing, since it is obvious that his acquaintance with Anatomy is very inaccurate; as, for example, he adopts the old ideas mentioned by Cheselden on the origin and termination of the lymphatics, instead of those which have been long universally admitted. Mr. Dallas employs a curious mode of establishing the utility and dependence on each other of the various parts which compose the body, by attempting to demonstrate, à priori, that those those parts must of necessity exist in a corporeal fabric,' in which was placed an immaterial part' to 'hold correspondence with other material beings by the intervention of the body.'Of this kind of speculation, we perceive neither the utility nor the truth. The different wants, for the provision of which var!ous organs were made, and the different modes in which those wants are supplied, were determined by the author of nature; and therefore, like other natural phænomena, they cannot be the subject of à priori reasoning. As Mr. D. acknowleges his obligations to the works of Cheselden and Hunter in the first part of his work, which is devoted to an anatomical display of the human frame: so in the second and third parts, which treat of the mental faculties and the passions, he confesses that he has availed himself of the writings of Watts, Burlamaqui, and Adam Smith; though he has not entirely depended on them, but has ventured to interweave a small treatise of his own. In displaying the anatomy of the mind, this compiler discovers no great metaphysical penetration: for he not only assigns to it more distinct faculties than it possesses, but he tells us that so absolutely free is the Will of the human spirit, that it may chuse to be directed by that which it judges to be the worst motive; or it may chuse to act contrary to every motive, or without any motive at all; and this last manner of acting is so well known and so common, that we have dignified it with a particular name, by calling it whim.' We are hence to un derstand that the whimsical man acts without any motive: but this mode of appreciating him is as much at variance with philosophy, as with the ordinary apprehensions of the world. A man of whim is not devoid of motives; he is only actuated by those which are singular or ridiculous. Besides, it is absurd to say that the Will in any instance decides without any motive at all. Some compensation is made for this metaphysical slip by the subsequent chapter on Conscience; and particularly by the third part, which is devoted to a consideration of the Passions. We do not mean to say that here, any more than in the foregoing parts, the analysis is perfect; on the contrary, had Mr. Dallas been more intimately acquainted with the writers on moral philosophy, he would have given a clearer view of the primary and of the compound passions-but, as a practical account of the operation of the passious, and as an essay intended to assist us in the moral knowlege and command of ourselves, we perused it with considerable satisfaction. The object of the whole is to shew that there is no essential viciousness in the passions, which is indeed, the doctrine of Aristotle: Павл |