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fpring or elafticity in a part of that mass, are the two general caufes of the variations of the barometer; now the primitive caufes that affect and modify the mafs and elasticity of a portion of the atmosphere, of a confiderable extent, are heat, cold, dryness, moisture, with their different combinations; and the influence of thefe caufes is difcuffed in the memoir now before us.
The effect of heat is the dilatation of the air. Many eminent men have alleged alfo, that heat augments the elasticity or fpring of the air, and from hence it is concluded, that heat must make the mercury rife in the barometer. Experience however proves the contrary. It is a general obfervation, that the barometer is often, nay regularly, higher in Winter than in Summer; it is moreover remarked, that, in Summer, the mercury defcends a little every day towards the hour of the greatest heat at noon, and M. de Luc joins his weighty teftimony to thofe of Meffrs. Bouguer and de la Condamine, in the confirmation of thefe obfervations. With respect to this point, our Academician adopts a well-known opinion, which comes to this that the air having, like all other bodies, a vis inertia, this prevents the rarefaction that it undergoes from the firft impreffion of the heat, from being inftantaneous; even when being fuddenly warmed, it can expand itself freely on all fides. Thus the augmentation of the spring or elafticity of the air, muft accompany the first moments of the expansion of the atmosphere, which is produced by a new degree of heat; and thus the heat will make the barometer rife, and that more or lefs as the portion of the atmosphere, fo warmed, is more or lefs dense or loaded with vapours; for the vapours are fufcep tible of a degree of elafticity fuperior to that of pure air. But when these first moments are paft, it is natural to think that the heat, continuing to act upon a portion of the atmosphere, fhould make the barometer defcend, and that for the following reafons: 1ft. Becaufe the expanfion of the air difperfes it on all fides, and thus the column of the atmosphere, which the heat rarifies, becomes lighter by lofing the quantity of air which the heat impels into the collateral columns. 2dly. Because the dilatation of the air weakens its fpring in proportion as that spring can expand itfelf with freedom in the rarified air: thus the influence of elafticity, which before fupported the mercury in the barometer, muft neceffarily diminish in the fame proportion.
From hence the author proceeds to confider the effect of cold on the barometer. Cold contracts and draws together the
• See the Memoirs of the Acad. of Sciences of Paris, for the year 1699, p. 101-125.
parts which it is the property of heat to feparate; and thus its natural effect, in the atmosphere, is, to condense the air, to compress its spring, and thus, ceteris paribus, to augment the preffion, which makes the mercury rife in the barometer.
As to the effects of dryness and moiflure on the air, our author obferves, that the elafticity of bodies encreases in dry weather, and that their fpring is relaxed and weakened by moisture. Confequently the drynefs of the air muft augment the preffion of the atmosphere, and make it fuftain an higher column of mercury, while moisture, by the effect now mentioned, mutt make mercury defcend. It is, however, neceffary to observe, with respect to the drynefs and moisture of the air, that if the latter diminishes the preffion of the air by relaxing its fpring, it, on the other hand, loads the air with watry particles, which, by their density, muft very confiderably augment its mass, so that it would be difficult to determine a priori, whether the moisture of the air be adapted to make the barometer rife or fall. The fame thing may be faid of drynefs, which difpels the watry particles that increased the weight of the air. So that there appears to be here a conflict between the effect of Spring and mafs, between elasticity and weight, and it is experience alone, which can affure us, that in this conflict, the effect of elasticity is much fuperior to that of weight. The ingenious Academician, after thefe obfervations, combines thefe four different ftates of the air, two by two, and points out the effects that must result from them with respect to the barometer. We must refer the reader to the memoir itself, for an account of the curious detail into which he enters, with a masterly spirit of fagacity and observation. We do not recollect any production in which this intricate, complicated, and difficult branch of natural philofophy, (the variations of the barometer) is treated with fuch depth, precifion, and perfpicuity, except the juftly celebrated work of M. de Luc, to which M. Beguelin does eminent justice, though he does not adopt all the principles and reasonings of that ingenious obferver of nature,
An Extract of the Meteorological Observations, made at Berlin, in
The obfervations and experiments, contained in this article, were made on vegetable, animal, and mineral fubftances. Each of these have furnished a great number of examples of the changes mentioned in the title of this memoir, which throw new light on the theory of colours, and lead to a variety of discoveries,
difcoveries, which may be of fingular ufe to the painter, the dyer, and the chemift.
MEMOIR I. Concerning the particular Integrals of Differential Equations. By M. de la Grange.
Only one hundred and feventy feven pages of Algebra. MEMOIR II. Concerning the Motion of the Nodufes of Planetary Orbits. By the Same.
Two Letters from M. D'Alembert to M. de la Grange. MEMOIR III. Demonftration of the Theorem of Bachet, and an Analysis of Numbers into Triangular and Square. By M. Beguelin.
MEMOIRS Concerning the Pole-Star, containing principally Refearches relative to the Science of Trigonometry. By M. Bernoulli.
SPECULATIVE PHILOSOPHY. MEMOIR I. Concerning the Mufcular and nervous Palfy, and the Method of curing it. By M. Pereboom.
This fubject was propofed as a problem to the Academy, by the late M. de la Condamine, with a premium annexed to its folution. The Author of this Memoir, who is a physician in North Holland, obtained the prize. The method he follows, in treating this difficult and complicated fubject, is judicious and clear, and the detail into which he enters, contains a wife and happy mixture of theory and experiment, the former of which justly entitles the memoir to a place in the clafs of fpeculative philofophy. To prepare the way for folving the problem, our Author gives a fuccinct account of the structure of the nerves, and particularly of thofe in the extremities of the body, which terminate in the skin or in the muscles, and thus become respectively the inftruments of mobility and fenfibility, the privation of which in any part of the bodily frame conftitutes a palfy. From hence he proceeds to distinguish three kinds of paralytic complaints, which he calls the Nervous, the Mufcular, and the Nerveo-Mufcular; the firft deftroys feeling without affecting motion; the fecond renders the part affected motionless without diminishing fenfibility or feeling; the third, which is a compound of the two firft, deftroys both motion and feeling, and takes place, when the regular communication of the members, by the means of the nerves, happens to be intercepted. Dr. Pereboom takes notice of the various caufes that produce these different kinds of the diforder under confideration, points out the circumftances in which this difference confifts, and illuftrates his obfervations by a great number of cafes and examples that have occurred to him in the course of his reading or practice.
The method of cure is the next object that employs the researches of this learned phyfician; but this fecond and important part of his memoir would fuffer effentially by being ab ridged.
MEMOIR II. Concerning the variable Nature of moral Perceptions, when they are confidered as connected with the diverfity of pfychological Syftems. By M. Beguelin.
The meaning of this title will perhaps be rendered more palpable, if we exprefs it thus in a free tranflation: Concerning the Diverfity that must take Place in Moral Perceptions and Maxims, if we confider them as influenced by the diverfity of Specu lative Opinions. If the actions of men, fays this ingenious Academician, were exactly determined by the dictates of reafon in each individual, it is evident that every man would follow a rule of morality proportioned to the meafure and extent of his reafon, the degree of his understanding, the weakness or ftrength of his intellectual view, and his peculiar manner of difcerning the various fitnefles and relations of things: and as the faculty of reasoning, and the degree of intelligence, acutenefs, and capacity, differ confiderably in different perfons, nay in the fame perfon, at different periods of life, there would be as many fyftems of morals as there are different men, if every individual formed his moral notions and maxims precitely upon the dictates of his own reafon, and made them fquare directly with his fpeculative opinions. But happily, for man and for fociety, (continues our author) the fuppofition is falle: man is not confiftent with himself, and nothing is more rare than to fee a perfect conformity between moral actions and intellectual principles. This inconfiftency M. Beguelin confiders as an happy arrangement of providential wifdom; for fince reafon is fo late in its appearance, and fo flow in its growth, that, during the short space of human life, it is able to take in but imperfect views of the nature, relations, and connexions of things, it would not have been defirable that fuch a creature as man fhould have had no other principle of approbation, volition or action, but the little theory, formed from the feeble and fcattered rays of his acquired knowledge.
But though man follows rarely in the tenor of his conduct, the fpeculative fyftems, in which his inquiries have terminated, our Author, nevertheless, thinks it may be worth while to enquire, to what moral and practical notions each fpeculative fyf tem would lead its followers, if they formed their notions and actions according to its principles. He thinks this enquiry important, becaufe he imagines the time may come, when this latter fuppofition will be realized, and when the defire of bappiness, which always directs the actions of men, and will act in concert with a diflint knowledge of all the means, by which
that happiness can only be attained. Then, fays he, man will be confiftent with himself: theory will be the lamp to practice, &c. &c. M. Beguelin fays this must happen one day; we hope it will; though we do not expect to fee that day here; fome ftreaks of its dawn may be observed at prefent, but it will shift its meridian luftre to another scene.
The principle from which our Academician fets out in his inquiry is this: that every man is irrefiftibly impelled to feek, what (according to his prefent manner of feeling and judging) appears to him the most adapted to render his fituation more agreeable. Now common fenfe muft perfuade us that true happiness muft embrace (in order to its exiftence) not the present moment only, but the whole of our duration, and that we reap a real advantage from facrificing the pleasure of a few minutes to the attainment of enjoyments, which though future, are more folid and permanent. Thus a bitter potion is swallowed to ensure health, or to recover it. Hence it follows that the notions of good and evil are variable according to the ideas we form of the duration of our existence; and the measure of that duration depends on the notions we entertain of the nature of the foul, and confequently on our fyftem of psychology.
In the entrance upon the inquiry propofed, M. Beguelin makes a diftinction between the opinions concerning the foul, which have no influence on morality or morals, and those which have, or ought naturally to have, a palpable one. In the former clafs he places the different fyftems of Ariftotle, Malebranche, Locke, and Leibnitz, and fhews that whether the foul be a Spirit, a monade, or an atom, whether it be fimple or extended, whether it operate by a phyfical influence, occafional causes, or a pre-established harmony, it matters not with refpect either to moral ideas or moral practice, provided that this foul be confidered, by the abettors of thefe different fyftems, as an intelligent and rational fubftance, created by the power and goodnels of a Supreme Being, who, inftead of destroying his own work, will lead it, by degrees, to all the perfection of which it is fufceptible, through an unbounded duration. But the cafe is different when we come to the second class of opinions: for on a supposition that the foul exifts by blind chance or a fatal neceffity, as there is no affurance of existence or felicity beyond the prefent moment, virtue will confift in enjoying the minute that paffes, and the terms honeft, decent, juft, moral, upright, are words evidently without meaning. Again-on the fuppofition that the foul perishes with the body, or that the former paffes, by tranfmigration, through an infinite feries of different states without the remembrance, in any one, of its preceding fituation, or any connexion between its fucceffive modes of existence, virtue can have little or no reality :-if the