that a proper distribution of rain and dry weather, with many other circumstances which it will not be necessary to mention, are probably of much greater consequence than the absolute quantity of light and heat derived from the sun. To this I shall only suggest, by way of answer, that those very circumstances of proper alternations of rain, dry weather, winds, or whatever else may contribute to favour vegetation in this climate. may possibly depend on a certain quantity of sun-beams, transmitted to us at proper times; but, this being a point which can only be ascertained by future observations, I forbear entering farther into a discussion of it.'

From the respect to which, as we have just observed, the labours and great successes of Dr. Herschel intitle him, we deemed it our duty to read his remarks with attention: but really it appears to us that if what he has attempted to shew might be deemed curious if proved, yet, as mere conjecture, it can scarcely excite either interest or amusement. Had a person hitherto unknown in philosophy composed this paper, it would probably not have been printed by the Royal Society; or, if it had appeared, it would soon have been consigned to that lunar region in which, amid "tomes of casuistry," the species of Aristotle, the films of Epicurus, the monads of Leibnitz, and the vortices of Descartes, repose in unenviable tranquillity. The true method of philosophizing is now too well understood, for us to be apprehensive that the purely conjectural specula tions of any one, however great his fame, will be prejudicial to science: but there is already a sufficiently strong proneness in human nature to indulge in hypotheses; and, as far as the weight of Dr. H.'s authority will prevail, he fosters and encourages this propensity. We do not approve what he has done, nor the spirit of his philosophy. Since he appears to be an advocate for hypotheses, he should shew what useful discovery in the works of nature have ever been produced by such speculations. He cannot be uninformed of the bad effects which they have caused: that is, into what fruitless disquisitions they have betrayed men of the greatest talents :-nor can he be ignorant why Bicon is esteemed the father of all true philosophy, because the sane maxims of that great man are now so familiar, as to be incorporated into common conversation. If the stupendous discoveries of Newton be not undeniable proofs, they are at least strong presumptive arguments, that his method of philosophizing was the true one. "Hypotheses non fingo," exclaimed that great disciple of Bacon; and if authority in these subjects be admitted, where shall we find authority equal to that of Newton?

Additional Observations tending to investigate the Symptoms of the variable Emission of the Light and Heat of the Sun; with Trials

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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. In this Appendix, Dr. H. abandons his former method of comparing the prices of wheat with the solar spots, and proposes to use the thermometrical observations, now regularly published in the Philosophical Transactions; which, he says, furnish us with a proper standard, with which the solar phanomena may be compared.

On an improved Reflecting Circle. By Joseph de Mendoza Rios, Esq. F.R.S.-After having described Mayer's and Borda's Instrument, with the advantages in observation which they were intended to introduce, and their imperfections, this gentleman gives an account of his own 'reflecting circle:' but the detail cannot be understood without plates, and not very easily with them.

Account of some Experiments on the Ascent of the Sap in Trees. In a Letter from Thomas Andrew Knight, Esq. to Sir Joseph Banks. The experiments here detailed were made on the crab-tree, the horse-chesnut, the vine, and the oak. In selecting a certain number of young trees in his nursery, early in the spring of 1799, Mr. Knight made circular incisions through the bark round one half of them, scraping off the external coat of the wood, and the other half were left in their natural state. On the ascent of the sap, they all shot with equal luxuriance: but he observed that the part of the stems which was below the incisions had scarcely any growth, while the parts above increased as rapidly as in the trees of which the bark had remained untouched. After midsummer, the stationary condition of the stem below the incisions was more manifest; and, having varied the experiments in every way that occurred to him, Mr. K. found the result to be uniformly the same whence he infers that the current of sap, which adds to the annual layer of wood in the stem, must descend through the bark from the young branches and leaves. Mr. Knight denies, with good reason, that the internal bark is converted into the alburnum, or that part of the wood which is vulgarly called the sap; and he regards the new matter, which enters into the internal part of the alburnum on its conversion into heart, or coloured wood, as of a nature different from the alburnum itself. In deducing his conclusions from the series of experiments here related, he observes that

The common tubes of the alburnum (which do not appear to have been distinguished from the central vessels) extend from the

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points of the annual shoots to the extremities of the roots, and up these tubes the sap most certainly ascends, impelled, I believe, by the agency of the silver grain. At the base of the buds, and in the soft and succulent part of the annual shoot, the alburnum, with the silver grain, ceases to act, and to exist; and here I believe, commences the action of the central vessels, with their appendages the spiral tubes. By these the sap is carried into the leaves, and exposed to the air and light; and here is seems to acquire (by what means I shall not attempt to decide) the power to generate the various inflammable substances that are found in the plant. It appears to be then brought back again, through the vessels of the leaf stalk, to the bark, and by that to be conveyed to every part of the tree, to add new matter and to compose its various organs for the succeeding season. When I have intentionally shaded the leaves, I have found that the quantity of alburnum deposited has been extremely small.'

These experiments tend to throw light on the theory of vegetation; and we hope that they will be prosecuted by the au Mo-y thor, who possesses an ingenious and investigating mind.

Observations and Experiments on Dr. James's Powder; with a Method of preparing, in the humid Way, a similar Substance. By Richard Chenevix, Esq. F. R.S-This gentleman remarks that it may be laid down as a general principle, that, in delicate experiments, whether analytical or synthetical, fire (that potent and once believed to be universal agent) is too precarious in its means, and too uncertain in its application, to be employed with full and constant success.' Allowing, therefore, that the experiments made by Dr. Pearson have fully elucidated the composition and nature of Dr. James's Powder, yet those very experiments serve to suggest that the mode of preparation is far from being the best which the present improved state of chemical knowlege may afford. Indeed, the advantages of humid operations are sufficiently known to chemists; and Scheele's method of preparing the Mercurius dulcis, or Calomel, is a striking example in Pharmaceutical Chemistry.

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Impressed with these ideas, Mr. Chenevix made some preliminary experiments, and at length found that the following preparation may be employed as a substitute for Dr. James's Powder, although made in the humid way :-viz. solve together, or separately, in the least possible portion of muriatic acid, equal parts of the white oxide of antimony (Algaroth powder) and of phosphate of lime; pour this solution gradually into distilled water, previously alkalizated by a sufficient quantity of ammonia.-A white and abundant precipitate will take place; which, well washed and dried, is the substitute I propose for Dr. James's Powder,' In cases in which a stronger preparation has been required, Mr. Chenevix has employed two parts of the oxide of antimony, and one of phosphate

phosphate of lime.-Several eminent medical gentlemen, who have made trial of this substance, agree that, in its general effects, it resembles Dr. James's Powder and the Pulvis Antimonialis of the Pharmacopoeia, but that it is milder, seldom producing nausea or vomiting, and may therefore be given in larger quantities.

An Account of some Galvanic Combinations, formed by the Ar rangement of single Metallic Plates and Fluids, analogous to the new Galvanic Apparatus of Mr. Velta. By Mr. Humphry Davy, Lecturer on Chemistry in the Royal Institution.—Mr. Davy

remarks that

All the Galvanic combinations analogous to the new apparatus of Mr. Volta, which have been heretofore described by experimentalists, consist (as far as my knowledge extends) of series containing at least two metallic substances, or one metal and charcoal, and a And it has been generally supposed, that their stratum of fluid. agencies are, in some measure, connected with the different powers But I have found that an ac of the metals to conduct electricity. cumulation of Galvanic influence, exactly similar to the accumulation in the common pile, may be produced by the arrange nent of single metallic plates, or arcs, with different strata of fluids.'

Some facts, which the author then relates, induced him to suppose

That the alternation of two metallic bodies with fluids, was essential to the production of accumulated Galvanic influence, only so far as it furnished two conducting surfaces of different degrees of Oxidability; and that this production would take place, if single metallic plates could be connected together by different fluids, in such a manner that one of their surfaces only should undergo oxidation, the arrangement being regular. On this supposition I made a number of experiments on different arrangements of single metals and fluids; and after many various processes, I was enabled to ascertain, that many of these arrangements could be made active, not only when oxidations, but likewise when other chemical changes were going on in some of their parts.'

Having made observations on the different combinations formed by single metallic plates and fluids, which he divides. into three classes, the ingenious author then proceeds to state that

In all the single metallic piles constructed with cloths, the action is very transient: the decomposition of the acids, and of the sulphurets, is generally completed in a few minutes; and, in consequence, the Galvanic influence ceases to be evolved. The arrangement of all the different series may, however, (by means of an apparatus constructed after the ideas of Count Rumford,) be made in such a manner as to give considerable permanency to their effects. This apparatus is a box, covered with cement incapable of conducting electricity,

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and composed of three pieces of mahogany, each containing grooves capable of receiving the edges of the different plates proper for composing the series. One half of these plates must be composed of horn, or glass, and the other half of metallic substances; and the conductors of electricity, and the non-conductors, must be alternately cemented into the grooves, so as to form water-tight cells.

، When the apparatus is used, these cells are filled, in the Galvanic order, with different solutions, according to the class of the combination ; and connected in pairs with each other, by slips of moistened cloth, carried over the non-conducting plates.

، A combination of fifty copper-plates, arranged in this manner, with weak solutions of nitrous acid, or nitrate of ammoniac, and sulphuret of potash, gives pretty strong shocks, rapidly evolves gas from water, and affects the condensing electrometer.

It does not lose its power of action for many hours; and, when this power is lost, it may be restored by the addition of small quantities of concentrated solutions of the proper chemical agents to the fluids in the different cells.

From two experiments made on copper and silver, it would ap pear, that the single metallic batteries act equally well, when the metals made use of are slightly alloyed, and when they are in a state of purity.'

A Continuation of the Experiments and Observations on the Light which is spontaneously emitted from various Bodies; with some Experiments and Observations on Solar Light, when imbibed by Canton's Phosphorus. By Nathaniel Hulme, M.D. F.R.S. & A.S.-In our review of the Phil. Trans. for 1800, we have had occasion to notice the experiments made by Dr. Hulme on the light emitted by various substances; and it is with plea sure that we find this gentleman continuing his ingenious researches. The present paper commences with the eleventh general section of his Experiments, which treats of the Effects of various aerial Fluids on Spontaneous Light.'-The Doctor first states that

The apparatus employed for experiments with any kind of air, unless otherwise expressed, consisted of the following parts: 1. A tea.saucer, holding about three ounces of water. 2, A widemouthed phial, which would contain about ten ounces of liquid, 3. A small wooden stand, composed of a slender pillar or pin, nearly four inches high, fixed into a round base, a little more than an inch in diameter, and half an inch thick. This stand was fastened by strong thread to the middle of a piece of flat lead, such as lines Chinese tea-chests, having holes in it to admit the thread; the lead was about three inches square, and doubled, to give it weight and stability. The top of the pillar was made pointed; and a round piece of cork, about an inch in diameter and half an inch thick, was fixed upon it, by means of a superficial hole bored in its under part with a gimlet.

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