vapour increases with its temperature. According to him, this capacity is doubled for every 27 degrees of heat added to air. Air at the temperature of 320 is capable of holdingth of its weight of vapour, at 59° it becomes capable of holding th part, at 86°th part, at 113th part, and at 140° th part. These estimates do not agree with those previously given by Mr. Dalton, from whose table it appears that the quantity of vapour which air can contain increases at a greater rate than Mr. Leslie makes it do. Mr. Leslie adopts the old opinion respecting the state of vapour in the atmosphere. He conceives that it is held in solution by the air precisely as salt is by water. He does not inform us of the reasons that induce him to adopt this opinion: but the result of his own experiments, if he had attended to it, would have shown him that the supposed analogy between the solvent power of water and air does not in reality exist. The solvent power of air, he says, is doubled by every additional 27 degrees of heat. But can any case be produced in which the solvent power of water increases in any similar proportion? I believe not. Mr. Leslie in this part of his book makes us acquainted with a number of instruments which he has invented for different purposes. The great principle upon which these instruments act is in most cases the same, though the information which they convey be different. This is probably the reason why they have been described all together. It would have been better if each instrument had been described in a separate chapter, or at least a separate section. These instruments are, 1. The Hygrometer. This instrument is merely the differential thermometer, having one ball covered with bibulous paper and silk, and the other made of coloured glass. The paper is moistened. The evaporation of this water produces cold, and this cold increases with the rapidity of the evaporation. Now this rapidity depends upon the comparative dryness of the surrounding air. Hence the lower the liquid falls in the tube of the hygrometer, or the greater cold produced, the drier is the air. Mr. Leslie gives us a curious collection of facts obtained by his observations with this instrument. 2. The Pyroscope.-This is an instrument for measuring the intensity of a fire. It is merely the differential thermometer with one of its balls covered with silver leaf, while the other is naked. The fire heats the naked ball, but not the silvered ball. Hence the liquid in the tube rises or falls according to the intensity of the fire, and of course marks that intensity. 3. The Photometer.-This is the differential thermometer, having one of its balls of colourless glass, the other of black glass. The light produces no effect upon the transparent ball, but it heats the black ball according to its intensity; and this heat, by depressing the liquid in the tube, marks the intensity of the light. Mr. Leslie has given a curious and valuable collection of facts established by means of this instrument; some of them published long ago in Nicholson's Journal; others new. I should have been sorry had these curious facts been omitted, which, in strict propriety, they ought to have been, as they have no connexion whatever with the subjects which the book professes to treat of. 4. The Atmometer.-This instrument has been already described in the Annals of Philosophy, vol. i. p. 467. It is an imperfect instrument; because it gives us no immediate information by inspecting it, as all the other instruments do. We must observe it twice in succession, and know the time between the two observations, before we can draw any conclusions from it. 5. Ivory Hygrometer.-This instrument has also been described in the Annals of Philosophy, vol. i. p. 468. The construction of it is highly ingenious, and does credit to Mr. Leslie's inventive powers: but it is from its very nature imperfect; and is always liable to alter by time. These imperfections were not unknown to Mr. Leslie, who points them out with great candour. III. Drying Power of different Bodies.-Mr. Leslie took different earths and various other bodies, dried them well before the fire, and then put them into well stopped phials. By putting a little of each into a large glass bottle along with a hygrometer, he ascertained the degree of dryness which it produced in the air. These results are curious, and unexpected. They are as follows: Alumina made the hygrometer stand at.. 84° Carbonate of lime.. Carbonate of barytes.. Carbonate of strontian Green-stone Sea sand with shells 75 70 The degree of dryness produced by the different soils he found proportional to the fertility of the soil. Hence he conjectures that the fertility depends upon this property. There can be no doubt that the fertility of soils is very much connected with the power which they possess of retaining the proper degree of moisture. Connected with these curious results are the following 100 grains of ivory attract from the air 7 grs. of humidity boxwood .... There is little difference between the effect produced upon the dryness of air by the pure earths and their carbonates; but the effect is greatly diminished by heating the earthy bodies red-hot. IV. Cold produced by Rarefaction, assisted by the absorbing Power of Sulphuric Acid. Mr. Leslie's method of freezing water by placing it under the receiver of an air-pump in a small vessel, while the greatest part of the bottom of the receiver is occupied by a shallow vessel of sulphuric acid, and exhausting the receiver, is known, I presume, to most of my readers. By drawing out the air, the rate of evaporation is accelerated. The sulphuric acid absorbs the vapour as fast as it is formed. Thus the evaporation is continued without intermission. The cold produced is sufficient to freeze the water in a very short time: indeed, it is so great that Mr. Leslie has even frozen mercury by means of it. Mr. Leslie describes the different experiments which he has made on this curious subject at considerable length, explains the theory of the congelation, points out the proper methods of proceeding, and the various important purposes to which the process may be applied. This part of the book is very interesting, and highly deserving the attention of all classes of readers. Indeed, the many valuable practical inferences which the author draws in different parts of his book, and the many useful purposes to which he conceives his instruments may be applied, give this little treatise a claim upon the attention of the nation in general, and entitle the author to the thanks, not only of men of science, but likewise of our manufacturers and agriculturists. The Philosophical Transactions for 1813, part ii. are published: they shall be noticed in a subsequent Number of the Annals of Philosophy. The Memoirs of the Imperial Academy of Sciences of St. Petersburgh for 1809, 1810, and 1811, have been received in London: they shall be likewise noticed in a future Number of the Annals of Philosophy. ARTICLE XI. Proceedings of Philosophical Societies. ROYAL SOCIETY. THE Royal Society resumed its meetings on Thursday, the 4th of November. A description of a sliding scale of chemical equivalents, contrived by Dr. Wollaston, was read. This contrivance is distinguished by all that sagacity which characterizes Dr. Wollaston, and cannot but be highly useful to the practical chemist. It is not easy to render the nature of this contrivance intelligible without an engraving, which I do not consider myself at liberty to give before the publication of the paper in the Philosophical Transactions; but the following observations will perhaps suggest some idea of it to those who are interested in practical chemistry. It was first observed by Richter that when two neutral salts are made to decompose each other, the neutrality of neither is disturbed. Thus if you dissolve 100 grains of sulphate of potash in water, and pour into the solution muriate of barytes in sufficient quantity to decompose the whole of the sulphate, two new neutral salts will be formed, namely, sulphate of barytes and muriate of potash. If into the muriate of potash thus formed a sufficient quantity of nitrate of silver be dropped to decompose it, two new neutral salts will be formed, namely, nitrate of potash and muriate of silver. Thus the same weight of potash has been united in succession with sulphuric, muriatic, and nitric acids. The weight of barytes that neutralized the muriatic acid neutralized likewise the weight of sulphuric acid combined with the potash which had neutralized the sulphuric acid. These observations of Richter were still farther generalized by Berthollet; but it is to Dalton that we owe the full generalization of the facts, and the explanation of them. He supposes that bodies unite atom to atom, and showed how the weights of the atoms of bodies might be determined. This subject, having been already explained at considerable length in the Annals of Philosophy, need not be farther insisted on here. Dr. Wollaston has divided the slider of a scale into the logarithmic spaces from 10 to 320, by a method famíliar to all who are acquainted with the nature of logarithms, or in a similar manner as the line of numbers is laid down in Gunter's scale. He considers 10 as representing the weight of an atom of oxygen. On both sides of the scale he has written the substances most familiar to chemists, viz. the acids, bases, water, and principal salts, each opposite to the number on the slide, which corre sponds with the weight of an atom of it. Suppose now we want to know how much oxygen combines with 200 mercury: bring 200 on the slide opposite to mercury on the scale; then over against oxygen on the slide will be found 16, the quantity of oxygen required. Suppose we want to know how much oxide of copper combines with 60 of sulphuric acid: bring sulphuric acid opposite to 60, and we shall find over against oxide of copper 61, the number required. The Sliding Rule is fitted to answer an infinite number of similar questions. Dr. Wollaston determined experimentally the composition of nitrate of potash, and found it composed of 68 acid +59 potash. His scale is referred to carbonate of lime, which he considers as the most exact standard of comparison that can be obtained. On Thursday, the 11th of November, part of the Croonian lecture on the Influence of the Nervous System on Muscular Motion, by B. C. Brodie, Esq. was read. This lecture began with a short historical account of the facts and opinions of former physiologists on this subject. The author then relates a number of experiments which he himself instituted still farther to advance the subject. He found that after the destruction of the lower part of the spinal marrow of a dog, the arterial blood of a horse injected into the lower extremities of the animal, after circulating through the limb, came out at the mouths of the veins dark coloured. He found that the lower extremities of a frog, treated in the same way, though deprived of voluntary motion, contracted by stimuli and by the galvanic influence. He found that the heart of a rabbit continued to beat with its usual regularity for some time after the blood-vessels had been emptied of their contents; but that the action of the heart was destroyed when an animal was strangled, showing clearly that the stimulus of the blood is not the exciting cause of the action of the heart. On Thursday, the 18th of November, the remainder of Mr. Brodie's paper on the Influence of the Nervous System on Muscular Motion, particularly of the Heart, was read. The author coneluded with some general inferences from the experiments detailed in the preceding part of his paper. Some farther experiments, comparing the Gregorian and Cassegrenian telescopes, by Brigade Major Cater, were also read. The author related a new experiment which he had made, and which confirmed the experiments detailed in his former paper on the superiority of the Cassegrenian above the Gregorian telescope. At the same meeting there was also read an analysis of a new species of copper ore, from India, by Dr. Thomson. This ore was discovered about 13 years ago by Dr. Heyne, at some dis |