fuses itself through a space occupied by another gas as it would do through a vacuum. As this theory has been for some time before the public, we shall not enter upon the consideration of it, we shall only remark, that the author fairly meets the objections that have been made to it, and with a laudable degree of candour and moderation, attempts to repel them. His principal antagonists are M. Berthollet, Dr. Thomson, Mr. Murray, and Mr. Gough. With respect to the constitution of liquids, they are considered as being like the gases, under the influence of the two opposite forces of attraction and repulsion, but existing nearly, if not altogether, in a state of equilibrium. Speaking of a fluid he observes that If any compressing force is applied, it yields, indeed, but in such a manner, as a strong spring would yield, when wound up almost to the highest pitch. When we attempt to separate one portion of liquid from another, the case is different here the attraction is the antagonist force, and that being balanced by the repulsion of the heat, a moderate force is capable of producing the separation. But even here we perceive the attractive force to prevail, there being a manifest cohesion of the particles.” The author now proceeds to consider the relation that subsists between fluids and gases, and in order to establish a characteristic mark of distinction between the chemical and mechanical action which they exert upon each other, he lays down the following posi tion. "When an elastic fluid is kept in contact with a liquid, if any change is perceived, either in the elasticity or any other property of the elastic fluid, so far the mutual action must be pronounced chemical: but if no change is perceived, either in the elasticity or any other property of the elastic fluid, then the mu "The relative weights of the ultimate particles, both of simple and compound bodies, the number of simple elementary particles which constitute one compound particle, and the number of less compound particles which enter into the formation of one more compound particle." He begins by laying down a serics of propositions concerning the manner in which combinations between the particles of bodies may be supposed to take place. When two bodies can be caused to combine only in one proportion, it may be presumed, that one particle or atom of each can only combine together, when two combinations take place between two bodies, that one atom of each form a binary compound, and that one atom of the one may combine with two atoms of the other, so as to produce a ternary compound. Proceeding upon this method of rea soning he deduces, that water is a binary compound of hydrogene and oxygene, that it consists of one that consequently the weight of atom of each of the elements, and these elements must be nearly as one to seven. Ammonia is in like manner a binary compound of hydrogene and azote, and the weights of the elements nearly as one to fire. With this chapter the first part of Mr. Dalton's work concludes. In giving an account of it we have done little more than lay before the reader some of the most important of the new doctrines which it contains, without attempting to form an estimate of their value, or to determine how far they are derived from a just process of reasoning. To have canvassed the merit of all Mr.Dalton's hypotheses, would have carried our remarks to an extent equal to that of the work itself. We presume, however, that we have given such a specimen of it, as to prove to our philosophical readers, that it is, in every respect, worthy of their attention. Although we cannot admit the force of many parts of Mr. Dalton's reasoning, yet his speculations are certainly original and ingenious, and promise to throw light upon some of the most intricate parts of chemical science. His style is unfortunately not engaging, he is so concise as frequently to be obscure, and sometimes to appear dogmatical. He is not happy in his illustrations, which sometimes tend rather to increase than to remove the intricacy of the subject. These however are comparatively but trifling defects, and although they may serve to repel the to repel the cursory reader, and will prevent the work from becoming popular, yet they cannot conceal its merits from those real lovers of science, who wish to go beyond the surface. ART. VII. A general Review of the Natural History of the Atmosphere, and of its Connection with the Sciences of Medicine and Agriculture; including an Essay on the Causes of Epidemical Diseases. By HENRY ROBERTSON, M. D. 2 vols. 8vo. THE important influence which the atmosphere exerts, not only on animal and vegetable life, but on the different parts of inanimate matter, render it an object of the first attention both to the physiologist and the chemist. A distinct treatise, appropriated to the history of its properties and operations, must therefore be considered as a valuable addition to the literature of the country, provided that the execution of the work in any respect correspond to the interest of the subject. How far this is the case with the treatise now under consideration, it is our business to enquire. Dr. Robertson divides his work into three parts, the subjects of which are, the physical properties of the atmosphere, its chemical properties, and its influence on animals and plants. Before he enters upon the physical properties of the atmosphere, he premises some general observations upon light, heat, and electricity, which, although they do not form an essential part of the atmosphere, yet are so constantly found attached to it, as to have an important influence upon its actions, both physical and chemical. The observations are short, and not particularly interesting. The physical properties of the atmos. phere are separately discussed at some length, and with considerable minuteness. Facts are brought forwards from a variety of sources, and we meet with an abstract of most of the opinions and hypotheses which have, at different times, been maintained with respect to the color, fluidity, density, and elasticity of atmospheric air. On many of these subjects philosophers are generally agreed, but there are some respecting which a great diversity of sentiment still prevails, or where the facts that have been brought forwards are not of so decisive a nature as to enable us to form a positive decision between the two opposing doctrines. In this state we ought perhaps to consider the question, which has lately been so much agitated, respecting the expansion of air by the addition of caloric. This has been the subject of investigation by some of the French chemists, and in this country by Mr. Daiton. He made use of an apparatus, which was as striking for its simplicity, as that of M. Jay-Lossac was for its complexity; they were both engaged in the enquiry at the same time, and the event was a complete coincidence in the results, although they were obtained by snch different methods of operation. They both found that equal additions of caloric cause an equal increase of bulk at all temperatures, and that all gases, in their pure state, possess an equal power of expansion. This coincicidence has been generally considered as a decided proof of the ac curacy of the deductions, and they have accordingly been regarded, by most chemists, as fundamental and incontrovertible positions. Dr. Robertson, however, seems inclined to adhere to the contrary doctrine, and yet he merely brings forwards, in a very general way, his reasons for dissenting from what appears so decided and powerful an argument in favor of the opposite conclusion. Our author takes an opportunity of entering very fully into the subject of the barometer; he gives an account of a number of observations that have been made upon it in different parts of the world, for the purpose of comparing the changes which the gravity of the atmosphere experiences in these respective situations; he relates the experiments that have been made with this instrument, for the purpose of ascertain ing the distance to which the atmosphere extends above the earth's surface, the use of the barometer in measuring the height of mountains, and he inquires into the cir cumstances which produce the rise and fall of the mercury. Upon this subject we have the following remarks. "It seems the barometer is not always affected by probable, that the range of the action of a solitary cause: its variat ons oftenest occur, from the combined influence of several agents: but these will be comprehended more readily, when treated of under the following heads. The first, and seemingly the most general cause, is a change in the temperature of the atmosphere, either of its density. The second cause de giving rise to an increase or diminution pends on the state of the air, in respect to the proportion of humidity it contains, and the state in which that humidity exists in it. In the third place, winds blowing from different points, are known to affect the range of the barometer in different ways. Electricity has been supposed to have a powerful influence over the condition of the atmosphere, and it has been therefore regarded of late years ing variations in the range of the baroas having a considerable effect in caus meter. And under the filth and last head, we have to investigate the lunar influence, as a cause conspiring to produce the same effect." With respect to the first of the the temperature of the atmosphere, causes which is here enumerated, we apprehend that it can have little effect, because if the quantity of air pressing upon the barometer be the same, it is of no consequence whether it be in a condensed or a rarefied state. We do not think that the humidity of the air can have much effect; until the water be actually dissolved, in which state it is no longer entitled to the appellation of humidity, it will not add to the pressure upon the mercury, and it is indeed found, that the mercury generally stands the lowest, when the air is the most loaded with moisture. The third cause that is assigned, winds blowing from different quarters, we must acknowledge to be so far connected with the state of the barometer, that according to the prevalence of particular winds, the instrument is raised or depressed; but the wind is only the remote cause, and the business of the natural philosopher is to detect what are the circumstances connected with an east wind which increase, and with a west wind which diminish, the weight of the atmosphere. The agency of the electric fluid, and the lunar influence, must be regarded merely as hypothetical; they may probably have some effect upon the barometer, but we do not find that our author is able to produce any proofs of their operation, or even to assign any plausible reason which should induce us to form this conclusion. A long section is occupied with remarks upon the temperature of the atmosphere, the source of its heat, the reason why the higher strata are colder than the lower, the correspondence which exists between the variations of temperature in different countries and their latitude, and the causes which make this correspondence to be not always accurate. The well known work of Mr. Kirwan is very largely employed in the formation of this chapter, and we have transcripts of most of his tables. About half of the first volume is on meteorology. It commences by a section on evaporation, and on the state in which water exists in the atmosphere, a subject which leads Dr. Robertson into a wide field of discussion. The experiments of Mr. Dalton are related, the different kinds of hygrometers are described, and the hypotheses are considered which have been advanced on the process of spontaneous evaporation. The author decides in favor of the opinion, that vapour owes its existence entirely to the agency of caloric, an opinion which is the one most generally adopted, and which perhaps posseses the fewest difficulties. As a specimen of his rea "Were vapour raised and retained in the atmosphere, in consequence of its power of dissolving water, spontaneous evaporation must have increased, according to the gravity and density of the air, and would have therefore been most considerable in the polar regions, or upon the summits of our highest mountains, where this process is not counteracted by the effects of pressure." This single sentence is, we apprehend, open to many objections. It does not follow that evaporation must increase with the gravity and density of the air, even although it depended upon an affinity between air and water. It may reasonably be conjectured, that the gravity and density of the air are themselves produced by the water already dissolved, so that the air would be thus necessarily less disposed to take up any additional quantity of fluid. Besides, even if the air were rendered heavier and denser by any independent cause, it is probable, that this very circumstance, by the additional pressure upon the water, would counteract the greater tendency to produce solution which the air might be supposed to derive from its greater concentration. With respect to the last clause of the sentence, we confess ourselves to be quite at a loss to know, why upon the hypothesis of solution, evapora tion ought to be greatest at the summits of the highest mountains. Surely Dr. Robertson does not suppose, that the air is either the most dense or the most heavy in these situations; we have only to refer him to a former part of his own work, in which he gives a long account of the method of measuring the heights of mountains, by ascer taining the diminution of the weight of the atmosphere at their summits. He goes on to observe, "Ice and snow have been found to decrease in bulk and weight, by evaporation, — a circumstance which does not seem easily accounted for by the above-mentioned theory; for, admitting that an affinity subsists between air and water, in its ordinary s ate, sufficient to enable the air to dissolve certain quanti ties of the water, it does not follow, that the same athinity should subsist under every change of this fluid." It certainly does not follow as a necessary consequence, that water should preserve the same affinity in its congealed as in its liquid state, but it is more probable that it should do so than that the contrary should take place, and the circumstance of ice being so readily evaporated, is undoubtedly more in favor of solution by chemical affinity than of solution by caloric. The following remarks we are sorry that we cannot comprehend. "Were the existence of vapour in the atmosphere owing to a solvent power of the air, it must have been raised in the form of water only. Vapour is a body possessing distinct properties, and totally dissimilar in its nature from what a solution of water in air would be." We wish the author had pointed out the distinct properties of vapour, and also those of a solution of water in air. In a work like the one now before us, which consists principally of facts and opinions taken from the writings of others, it is extremely important that the author should be able to select, from the heap of mat ter which must accumulate under his hands, such alone as are worthy of his attention. Dr. Robertson, however, does not appear to us to have this happy talent of discrimination, he rather seems to us to possess an understanding of that description which swallows all that is presented to it, As a proof of our position we shall adduce a paragraph on dew. "The water of which dew is formed, has been found to possess properties di ferent from rain water in general, and e- De Crete the bay laurel sheds its effluvia so far around, as frequently to destroy those who unwarily fall asleep under its shade. The pernicious effects of the vapour exhaled from the boa-uppas tree, is likewise well known to the inhabitants of Java. The heavy dews which fall in Egypt have likewise been assigned, by every of that country, as a chief cause of the ophthalmia, which is so frequent among st writer on the climate and diseases its inhabitants." We scarcely expected to have seen Borelli quoted in the 19th cenfact, nor do we consider de Tott as tury as an evidence for a chemical the most fortunate authority to adduce in proof of any doubtful or contested point. With respect to the Upas tree, we believe that the inhabitants of Java never heard of its existence, and even admitting the truth of the facts that are relat ed respecting its destructive effects, it has no more to do with dew than the poison of arsenic. We must althat the pernicious effects of the so, by the way, absolutely deny dew in the West Indies or in Egypt, depends upon any thing peculiar in its chemical composition. |