Remarks on the Formation of Nitric Acid, which happens during the reciprocal Decomposition of the Oxyd of Mercury, and of Ammoniac. By the same.

M. FOURCROY had observed that the reduction of mercury to a metallic form, by the decomposition of ammoniac, mentioned in the former paper, was accompanied with some degree of effervescence, owing to the disengagement of azotic gas; the small quantity of this gas, which was actually evolved, surprised him; and he conceived that the greater part of it must have entered into some new combination. He found, by repeated experiments, that the nitric acid had been formed by a portion of the azote from the ammoniac uniting with a portion of the oxygen of the oxyd. In conjunction with M. Vauquelin, the author discovered another method of producing the nitric acid, by pouring concentrated sulphuric acid on the liquid prussiat of soda, or on the caustic mineral alkali, saturated with the colouring matter of Prussian blue; the nitric acid gas is disengaged with effervescence, and with the sensible smell of the acid: the red colour may even be given to the vapour by mixing nitrous gas with atmospheric air.

Memoir on the Combustion of Hydrogenous Gas in close Vessels. By M. M. FOURCROY, VAUQUELIN, and A. SEGUin.

These experiments were undertaken with the view of determining the exact proportion of the component parts of pure water. A copious and elaborate detail is here presented, which does not admit of abridgment, and which could not be understood without the plates and tables. The result of the various processes, which were conducted with almost unexampled minuteness and accuracy, is that the bulk of oxygen is to that of hydrogenous gas, requisite to constitute water, as 1 to 2, c62. It is the less necessary to enter into all the details of these celebrated experiments, as the public have already been put in possession of the most remarkable circumstances attending them. First Memoir on the Insensible Perspiration of Animals. By M.M. A. SEGUIN and LAVOISIER.

The modern theory of chemical phenomena has been successfully applied to explain the changes which take place during respiration, A series of experiments is here announced for extending our views of the animal oeconomy, by combining observation with chemical pathology; and by attentive discrimination of the different sources of evaporation from the body, which had been neglected by Sanctorius and his successors. The subject well deserves prosecution: but the lamented name of LAVOISIER, which stands at the head of this memoir, renews our regret for the loss which science has sustained. We trust, however,

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however, that his associates will not lose sight of the encou raging prospects of improving physiology, which are here opened to them.

Observations on the Defects of the Cupelling Furnace of the Assayists. By B. G. SAGE.

This short paper points out the necessity of making small openings in the muffles, and of altering the form of the cupelling furnace, which does not appear to have shared in the recent improvement of so many other parts of chemistry.

Observations on the Structure and Growth of Timber. By L. C. DAUBENTON.

In this memoir, the growth of the palm-tree is described as very different from that of other trees. Instead of growing by the addition of annual layers, which present the appearance of so many concentric circles, when the trunk is divided transversely, the palm-tree increases by dark coloured, longitudinal filaments; which shew, on the transverse section, like black spots.Wood, which is thus formed, M. DAUBENTON distinguishes by the name of lignum fasciculatum; and he points out several other examples of it, in the genus Calamus.

Memoir on the Quercus Ballota, or Sweet Acorn Oak of Mount Atlas. By M. DESFONTAINES.

From the time of Pliny to the present period, the existence of the oak which produces sweet acorns has been known to botanists but the plant itself has not been thoroughly described. Clusius had mentioned and even given the figure of a Spanish oak, which he calls Ilex Major, and of which the acorns are sweet, and which in all probability is the plant described in this memoir. His description, however, is too short to draw any certain conclusion as to the identity of the plant.

The Quercus Ballota here described is found in Barbary, on the mountains of which country it forms in many places immense forests. It grows to the size of 30 or 40 feet; its wood is compact; the fruit is sweet and nourishing; and the specific characters place this species between the Quercus Ilex L. and the Quercus Suber L. M. DESFONTAINES is persuaded that this oak could easily be naturalized in France, particularly in the southern provinces, where it would prove a valuable acquisition.

Observations on the Rhomboidal Calcareous Spar found in the Quarries of Sandstone at Fontainebleau. By M. SAGE.

The crystallized calcareous sandstone of Fontainebleau is well known to mineralogists. The form of these crystals is the same with those of calcareous spar, and this substance composes

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poses the % of the crystallized sandstone of Fontainebleau. M. SAGE was inclined to suppose that the form which these crystals assumed was owing to the calcareous spar; and that some rhomboidal crystals of pure calcareous spar, lately found at Fontainebleau in the same quarries in which the crystallized sandstone was obtained, are a confirmation of his conjecture.

Analysis of a Terreous Ore of Zinc, from Gazimour in Siberia. By M. SAGE.

Very little is said respecting this ore; yet, notwithstanding the extreme conciseness of the analysis, the paper is interesting in a statistical light, on account of the details which it contains concerning the importation of metallic substances into France; and which is valued by the author at twenty-five mil lions of French livres yearly.

The volume also contains a memoir by M. Haix on crystals; on which we must forbear to enlarge, as our observations on this work have already extended to a great length. We must now, therefore, take our leave of it, by expressing our regret at bidding a FINAL adieu to the Academy of Sciences! May the Society, whose labours are to succeed it, form some compensation for the loss which the literary world experiences in the dissolution of its highly respectable Parisian Friend!

ART. X. Traité Analytique, &c. i e. An Analytical Treatise on the Resistance of Solids; and on Solids of equal Resistance; with a Series of new Experiments on the specific Force and Elasticity of Oak and Fir. By P. S. GIRARD, Civil Engineer. 4to. pp. 340, and 9 Plates. Paris, 1798. London, imported by De Boffe.

IN

Nour last Appendix, time allowed us to take only a short notice of this work: but we have since perused it with great attention, and we have much to say in its praise; for we have received from it no inconsiderable augmentation of our stock of knowlege.

In the Advertisement prefixed to the work, we are told that it was begun in the year 1787; and that some of the propositions contained in it were delivered in the author's Memoir on Sluices, which gained the prize of the Academy, and was published in their Transactions.

The present treatise is distributed into five parts, an introduction, and four sections. In the former, M. GIRARD gives an historical and critical account of the experiments and analytical researches, which have been made on the subject of the resistance of solids, from the time of Galileo to the present day. Galileo,

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Galileo, who is justly considered as the founder of the science of mechanics, was induced to make the resistance of solids the object of his meditations, by viewing the different machines in the workshops of the arsenal of Venice.

The figure and constitution of material bodies are so variable and irregular, subject to so many accidents, and so difficult of analysis, that, in questions concerning them, we cannot with any precision fix what are the true elements which should enter into the discussion. "The subtlety of nature," as Lord Bacon says, "conquers the subtlety of man by so many degrees," that, in our hypothesis, we can only approximate to the real state of the circumstances which present themselves in physical objects. Of the causes which operate in nature, some are so complicated that their separate influence cannot be assigned; some are so irregular that no law is able to circumscribe their effects: but, if each cause could be distinctly assigned, an hypothesis which comprehended all would be unfit for the purposes of analytical research, since such an hypothesis would lead to formulas beyond the skill of the mathematician to reduce or integrate.

That the resistance of solids might be subjected to calcula tion, Galileo supposed first that bodies were composed of solid fibres, parallel to one another; he then inquired what was the force with which they resist the action of a power stretching them in a direction parallel to their length, and found that it was proportional to the number of integral fibres ;-next, considering the fibres as subjected to an effort perpendicular to their length, he found that the resistance of the integral fibres was proportional to their sum multiplied by an arm of a lever, which is always a certain part of the vertical dimensions of a solid in the plane of its rupture. All hypotheses on this property of bodies accord in this point. The distinctive character of Galileo's hypothesis consists in this, that the resistance of each of the fibres is independent of their quantity of extension at the instant of their rupture. Galileo applied his reasoning to the solution of some of the processes of nature, and shewed that the stalks of certain plants, and the bones of animals, united with a determinatc force the greatest possible lightness.

The theory of solids, so useful to the arts, is likewise due to the genius of this philosopher. M. GIRARD states and com ments on this theory, with clearness and judgment:

The weight with which a solid is charged perpendicularly to its length endeavours to break it, not only at its base of fracture adjacent to its point of support, but moreover at all the sections parallel to this base. In order, then, that the rupture may not happen, it is necessary that each of these sections should have such dimensions,

that

that its resistance be not overcome by the effort of the corresponding power; and, as a superabundant resistance would be a lost and useless force, it follows that the most advantageous form which can be given to a solid so disposed is that which makes it resist, equally, at each point of its length, to the effort of the weight with which it is charged. In forming bodies of equal resistance, we form them of the least volume; and thus we may act conformably to the views of nature, whose operations seem all to be carried into effect with the greatest economy of means....

The distinction of the productions of nature from those of art appears in this;-in the former, the cause and effect essentially agree; the one cannot undergo any modification without the other experiencing some change; or, to speak more precisely, a new effect always results from a new cause :-in the productions of human industry, on the contrary, there is no necessary proportion between the effect and cause: if, for example, a determinate weight is to be raised, it is indifferent whether we use the thread which has precisely the adequate force, or the cable which has a superabundant force; while, if the same weight had rested naturally suspended, it would have done so by means of fibres peculiarly appropriated in their, organization to this object, and whose disposition would have presented the most advantageous form. Perfection resides in a single point, at which nature arrives without effort; while man is obliged, in repeated trials, to pass over an immense space which separates him from it.

By the meditation of these operations, we recognize the boundless sagacity which directs them; and often we lift up a corner of the veil that conceals from us the eternal laws to which nature is sub ject. Galileo was thus conducted "as by the hand" (to use his own expression) to discover the uniform acceleration of heavy bodies. and Maupertuis was thus led to discover the laws of the refraction of light and of the shock of bodies; for the principle of the least action established by this geometrician is, in fact, only the summary enunciation of the ideas conceived before him by Galileo. Euler, having meditated on these ideas, has generalised the principle of Maupertuis, by his application of it to the motion of projectiles; and lastly, La Grange, regarding this principle not so much as a metaphysical truth, as a simple and natural result of the laws of mechanics, has given to it in these latter times a new degree of extension.

The theory of the solids of equal resistance is in truth only an application of the same principle; since, among an infinite number of bodies of a determinate resistance, the solids of equal resistance are those which contain the least quantity of matter. To reduce to this form, then, as much as circumstances permit, all bodies used in the construction of mach intended to augment our forces, is to approach to the perfection which so distinctly characterises all the works of nature: in a word, it is to act conformably to her views.

• In the mechanism of the animal economy, has not nature, then, forgotten so advantageous a form? The feathers of birds offer to us a sensible example. We must consider them as solids inserted at their extremities, and employed to beat the air during the flight of the bird: since the air re-acts on them, the case is the same as if they were sub