a man whose views were weak and superficial indeed, compared with the force and profundity of his own. While he continues in this temper, we may venture to assure him, he will make little progress in political economy, though he seems not to be deficient either in acuteness or ingenuity.

Art. V. An Elementary Treatise on Natural Philosophy. Translated from the French of M. R. -J. Haüy, Professor of Mineralogy at the Museum of Natural History (Paris) &c. &c. &c. By Olinthus Gregory, A. M. of the Royal Military Academy, Woolwich. With Notes by the Translator. 2 vols. 8vo. pp. 435, 427, 24 Plates. Price 17. 4s. bds. Kearsley. 1807.

TO accumulate facts and to register observations is an easy

task; perseverance and a very moderate portion of intellect will suffice to fill the pages of a common place book; but to exhibit a connected view of the phenomena of nature, to combine them scientifically, and to reason upon them justlyin short, to treat them philosophically, is the peculiar prerogative of genius. This excellent design has been executed by M. Haüy, in a manner the most honourable to his abilities. We certainly have not been uniformly pleased with his performance, in which there are both errors and deficiencies deserving of censure; but its merits are so great and so numerous, and its failings so few, some of them even are so brilliant, that we hesitate not to assure our readers there is more originality of manner and more vigour of intellect discoverable in the Traité de Physique of M. Haüy, than in any other elementary treatise of Natural Philosophy which has for many years made its appearance in Britain. The Translator has executed his task with fidelity and skill; the public are well acquainted with his talents, and will doubtless feel much indebted to him for presenting so valuable a production to their notice.

In this country, M. Haüy has been known chiefly by his researches into the nature and laws of crystallization; and his theory has deservedly ranked highest among those which have been devised for explaining that curious and interesting subject. The present volumes constitute part of a course of instruction for the French National Lyceum, in conjunction with Biot's Astronomy and Francœur's Mechanics.

M. Haüy's object, in composing this work,' says the translator, was not to produce a compilation of earlier performances, a collection of insulated dissertations, in which every former theory shall be exhibited, but none examined; it was rather to give a cast of unity to this department of human knowledge, to present Natural Philosophy though in an abridged, yet in a complete form, to free it from a great number of superfluities with which it had been overcharged, and to develope scarcely any but theories now solidly established, though perhans nai ted that he might be the better able to pla

Physics in the situation it ought to occupy, by assigning their due portions to the comparatively recent branches of Magnetism, Electricity, Galvanism, Crystallography, &c., and by enlarging those boundaries which some modern authors seem to have established upon too narrow a space.' Pref. p. vi.

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Mr. Gregory, it seems, had been for some time intending to complete a course of Natural Philosophy, by taking up those subjects which were necessarily omitted in his works on Astromy and Mechanics*, when he met with the Traité de Physique; this part of his design,' he modestly observes, has been executed by M. Haüy in a manner so far superior to any thing he could himself have accomplished, that he is persuaded he shall be rendering the public a more essential benefit by laying before them the present treatise, than by offering any original performance of his own embracing the same subjects.'

M. Hauy discovers the genuine spirit of philosophy throughout his introduction, which is not less commendable for the eloquence of its style than for the value of its matter; he sketches, with a masterly hand, the outline of his plan; and allots to the different parts of his subject their relative extent, situation, and importance. The representation he has given of the method to be followed in philosophical investigation, is just and luminous. The distinction between system and theory is forcibly expressed.

The object of a theory is to connect to a general fact, or to the least possible number of general facts, all the particular facts which seem to be dependent... But a system, such as... ought to be banished from natural philosophy, consists in a purely gratuitous supposition to which we

endeavour to confine the course of nature. It is a vortex, it is an effluvium of subtile matter; it is any thing we please, for all is possible to the imagination. By the aid of this supposition, which always goes beyond the facts given by observation, all is explained in a vague and loose manner, satisfactory notwithstanding in this, that it does not cost more to comprehend it than to invent it originally. Hence the system proceeds as at hazard; always wandering near the point; but incapable of determining any fact, with that precision, that rigour, which constitutes the character of the true theory: in a word, the system is the romance of nature, while the theory is its history, which, without ever ceasing to be faithful to truth, embraces at once the past, the present, and the future.'

The word System, however, may be properly used in scientific language in certain acceptations: as when it is employed by mathematicians to express the aggregate of bodies held in connection by their mutual actions, by astronomers to denote the arrangement of the celestial bodies about a common centre, and by naturalists in allusion to those methodical dis

*See Ecl. Rev. Vol. III. 971.

tributions which they find it advantageous to make of the objects of their study.

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The work itself, as is usual and requisite, commences with an enumeration and account of the general properties of bodies. These properties are distributed into two classes, in the first of which are placed, those which attach to bodies 'considered simply as assemblages of material particles,' such as Extension, Impenetrability, and Divisibility; and in the second class are included, those properties which depend upon certain forces that solicit or impel bodies,' of which six are enumerated, viz. Mobility, Hardness, Elasticity and Ductility, Gravity, Crystallization, Heat. Under these heads we find much perspicuous and accurate description, valuable information, and acute reasoning, with occasional excursions into dependent or collateral topics. In treating of Crystallization, which the author defines the regular arrangement. of the molecule of certain bodies under geometrical forms,' M. Haüy developes the principles of his own theory, which is particularly excellent for the precision of its language, and for the number and accuracy of the observations on which it is founded. The subject of Heat, considered in its tendency to equilibrium, and in the effects it produces upon bodies, is investigated with ability; and good descriptions are given of the various kinds of Thermometers invented to measure its intensity, and of the Calorimeter to ascertain its specific quantity. The part relating to Combustion is much too concise, and the author takes up without qualification or discrimination the theory of Lavoisier: the deficiency in this subject is partly supplied by a valuable note of Mr. Gregory's. In discussing the question whether caloric be the effect of intestine motion, or whether it be in itself a real substance, our author accedes to the latter opinion, or rather adopts the language conformable to it, regarding it solely as an hypothesis more proper to assist the conception of phenomena, and more commodious in expression.'

With laudable circumspection Mr. Haüy remarks,

• We shall adopt a like method on all similar occasions,...not for the purpose of expressing beings whose existence is not sufficiently demonstrated, but to present, by the imagination, a subject to the action of known forces that contribute to the production of the phenomena. Still, however, we shall not lose sight of the difference between the actual fluids which we can feel, and can confine in vessels; and those agents respecting the existence of which observations have not, as yet, completely satisfied We do not, therefore, place them in nature, but solely in the theory, since they possess the advantage, when judiciously selected, of representing results faithfully, of furnishing a satisfactory explication, and even of aiding us to foresee future appearances; so that if they are not the true agents employed by nature in the production of phenomena, they are reputed as occupying their place and existing as their equivalents.' p. 103,

us.

The next object of consideration is Water, in its various states of liquidity, ice, and vapour; and, in connection with it, hygrometry, capillary tubes, congelation of mercury, and steam engines. In explaining the phenomena of capillary tubes, a term is employed which, though often used on the continent, has seldom been adopted in England: this is the law of continuity, to which, it is said, the phenomena in question are subjected. This law is defined, in a note by the translator, to be that by which variable quantities passing from one magnitude to another, pass through all the intermediate magnitudes, without ever passing over any of them abruptly. Some excellent illustrations of this law are added from Boscovich, together with his demonstration of its universality; it is here applied to a familiar phenomenon, which some have inadvertently ascribed to the general law of attraction;

It is likewise to actions of the same kind as those that produce the phenomena of capillary tubes, that we ought to attribute the mo ions by the aid of which two small bodies floating upon a fruid, at a little distance from one another, approach till they are in contact, or fly from one according to circumstances. These bodies being among those which are in a state of solidity, cannot exert one upon another any sensible attractions or repulsions; so that what occurs in the motions now under consideration is solely due to the action of the particles of the liquid in contact with the same bodies.'

The subject of capillary attraction is pursued with much ingenuity by our author, who has availed himself of Clairault's investigation; but Mr. Gregory prefers, and with reason, the theory of Laplace, an account of which he has given

in two notes.

The following distinction should be remembered.

'The phenomenon which consists in the passage of a body from the state of liquidity to that of vapour, takes the name of vaporisation when it is solely due to the action of caloric, and that of evaporation when the air intervenes in its production, by the affinity which it exercises towards the particles of the vapour.

We have observed that the term affinity is, in several places, used as synonymous with cohesion, to signify the cause of adherence between the molecule of homogeneous bodies: in the second volume p. 178, it is employed in its true chemical sense to denote "the tendency which the constituent particles of some bodies have to unite with those of other bodies."

Of steam-engines a well-written history is given; but as it is too brief to be completely satisfactory, the translator has referred to other sources of information. He has also advanced the claims of two of our countrymen, which M. Hauy had smitted, to important discoveries-that of Cavendish, relative

to the composition of water, and that of Canton, relative to its compressibility. In many other instances, we acknowledge the patriotic zeal with which he has vindicated the fame of British discoverers from invidious misrepresentations.

We are next presented with an account of atmospheric air, and its most constant properties of heaviness, and elasticity, with the phenomena produced by its action; the effects of caloric upon this fluid, in dilating it, or increasing its elasticity; its efficacy in evaporation, by dissolving water and uniting with it; and, lastly, the nature and propagation of sounds, of which air is the vehicle. This division of the work includes also the following subjects, as naturally and intimately connected with the preceding the barometer, and its application to the measurement of heights, &c.; pumps, and their mode of action; the syphon; winds, and aqueous meteors; origin of fountains; air-balloons; comparison of sounds; musical temperament; theory of wind and stringed instruments, &c. Much ingenuity is evinced in the treatment of these articles; the facts are well selected and detailed; and the illustrations, for the most part, are very appropriate. A curious fact, observable in the action of caloric upon air, is the uniformity of the law to which the dilatation of different kinds of air or gas is subjected. Gay Lussac examined this point with considerable attention, and found that, whether the gases he employed were soluble or insoluble, the effect was the same; atmospheric air, hydrogenous, oxygenous, and azotic gas; carbonic acid gas, muriatic acid gas, sulphureous and nitrous gas, and the vapour of sulphurated ether, furnished results absolutely similar, as to the progress of dilatation between the same limits of temperature. These results accord with the experiments which were made about the same time in England, by Dalton. Another coincidence, more remarkable in theory than the preceding one in practice, occurs on the subject of evaporation. The theory of Le Roi, adopted by M. Haüy, agrees so exactly with that of Dr. Hamilton, referred to by the translator, not only in its leading doctrine of solution, but in several of its particulars, that it becomes difficult, at first sight, to suppress the idea of collusion or of plagiarism. Le Roi's theory was published in 1751, and Hamilton's not before 1765; Dr. Hamilton assures us, however, that he has not represented any thing as new, which he was conscious had ever been proposed, even conjecturally, by any one before him; and as the memoirs of foreign academies were not so familiar to English readers, and the discoveries of philosophers were not then propagated with so much facility, as they are now, by means of journals, magazines, and reviews, we can easily give credit to this declara