7. Experiments No. 2, 5, 6 and 7, the greatest number of those which may be regarded as conformable to the third place of decimals, give a mean of .11361.

8. Table VII. contains 3 experiments made in each of the two vessels used in that series, which were performed under a cone of tinned iron to defend the water-vessel from radiated heat, but as it was set loosely on the table which supported the container, it did not prevent the motion of air around the latter, and as the experiments made in this manner terminated from three to four degrees above the temperature of the room, there is reason to suppose that the results of those 6 experiments are all below the truth. Taking then the other six of this table, which were made with the same precautions as those in table V. and VI., we have as the mean result in the thicker glass .112952; and that in the thinner .113631.

9. The two experiments which conform entirely with each other, for the thicker vessel, give the specific heat .113498, and the two for the thinner .113489.

10. The mean of all the results, including both those obtained with the cone, and those with the cylinder of tinned iron, to defend the water vessel, give a mean result of .112350, and the six rejected experiments taken by themselves .111511.

11. In the thinner copper vessel, the trials as recorded in table VIII, exhibit the mean of seven results equal to .115752.

12. Rejecting those which began and ended too low, and hence gained heat from the air, as well as from the iron, we have in the thinner vessel .112577 as the mean of four experiments which are considered comparable.

13. In the same table eleven experiments in the thicker vessel indicate a mean of .114900.

14. With the same jar, seven experiments which are considered comparable, give a result equal to .113261.

15. In the thick sheet iron cylinder, weighing 5167 grains, we find by table IX., that the mean of five trials gave a result = .113253.

16. In the same vessel, three experiments which differ only in the 4th place of decimals give a mean specific heat = .113622.

17. In the thinner sheet iron jar weighing 1733 grains, nine trials gave a mean result of .112972.

18. Three experiments in this vessel which differ only in the fourth place of decimals, give a mean of .113365.

The following table embraces a synoptical view of the experiments on specific heat thus far detailed.

ter vessel was now filled with melted tin, instead of mercury, as well to avoid the inconvenience from mercurial fumes, as to obtain the specific heat of iron at a second fixed temperature, the melting point of tin. It needs scarcely be mentioned, that the same degree of exactness in the accordance of experiments at temperatures above 400°, as at 212°, is hardly to be expected. Table XI. (Frank. Jour., vol. 19, p. 158) exhibits a number of trials made in the manner just pointed out.* A certain amount of error may possibly have been introduced into these experiments by the want of uniformity throughout the mass of melted tin; for, after withdrawing the standard piece and lowering the thermometer to the bottom of M, it was found that a difference of a few degrees, was a possible occurrence; but as the bulb of the mercurial thermometer, which marked the temperature of the melted tin, was generally kept at the same level with the centre of the standard piece, any difference between the two, must be trifling in amount.

The last arrangement for demonstrating the specific heat of iron, was in the nature of a verification of the methods already detailed, by means of a direct application of the standard piece to the purpose for which it is ordinarily employed-that of generating vapour instead of heating water.

It was, for this purpose, heated as before described, in the bath of melted tin to such temperatures, above 212°, as were deemed necessary, and immediately plunged into boiling water. The effect produced, was now ascertained by multiplying together the weight of vapour generated, and the latent heat of steam; while the cause was found in the weight of iron, its specific heat and the temperature which it expended. The shield to defend the iron in transitu was employed, and the other precautions to avoid error were still persevered in. The results will be found in table XIII. (Frank, Jour., vol. 19, p. 165.)

Before proceeding, however, with the detail of those trials, it is necessary to state the mode of ascertaining the latent heat of the vapour of water, which enters as an essential element into the calculations of that table. It will be perceived that the prin

*It will be evident on a comparison of this table with those which have preceded, that the general law observed by Petit and Dulong (Ann. de Chim. et de Phys., vol. VII.) of an increase of specific heat by increase of temperature, when the method of heating water is employed, is confirmed by these results; but experiments on the production of vapour hereafter given, exhibit a very striking conformity, in regard to specific heat, with those made below 212 deg.

ciple of the method is similar to that of Count Rumford.

Apparatus for the latent heat of vapour. -The apparatus by which the latent heat of vapour was examined, is represented in Plate 8, in which A is a cylindrical vessel to contain water; B a larger cylinder formed of pasteboard, higher than the preceding, surrounding and defending it from the air; C is a stand of charcoal on which the vessel rests; D is a vessel of tinned iron, 14 inches high by 9 in diameter, to prevent the vessel F (the same which has already been described as the boiler of the steam pyrometer,) from affecting by radiation the temperature of A. P is a sheet of tinned iron, attached in a vertical position to the edge of the table T, serving still further to defend A from the influence of radiation from the boiler or steam pipe. S is a cylindrical piece of cast iron, having round its lower base a ridge r, adapted to retain a hold of the small hook h, within the copper case L, intended to receive it when hot. From the upper conical part of this case rises a pipe 9. quarter of an inch in diameter, curved into a semi-circle at the top to dip under water. Within the curved part is a stopcock K, adapted to regulate, or entirely to prevent when required, the flow of steam from L. At q is an enlargement of the pipe g, with a funnel-shaped tube to receive the bulb of a thermometer e, sustained and made tight by packing around the lower part of its stem. The purpose of this thermometer is to mark the temperature of the effluent steam. w is a handle, formed by a number of folds of flannel made fast to the pipe. r is a thick roll of cloth surrounding g, and preventing the escape of vapour exterior to the tube. The thermometer o marked the temperature of the apartment in the immediate vicinity of the apparatus. i gave that within the pasteboard case, while t gave the temperature of the water in A. (To be continued.)

by a mixture of oxygen gas with it. The former particular we esteem to be of great importance, for cold being perhaps the most powerful agent in destroying life, it cannot be less necessary to communicate warmth to the interior, than by baths and other means, to the surface of the body. The Royal Humane Society will assuredly hasten to add this to their other means of recovery. We would advise Mr. Read to furnish with the apparatus, air tight bags, which being applied to the extremities, and the air exhausted by the same instrument, would tend to relieve congestion of blood in the head and other parts, and facilitate its circulation.

Among other interesting articles on the table, was a section of a nettle, discovered by Mr. Cunningham, the Australian traveller, at Morton Bay, north of Sydney, growing 100 feet high, and having leaves (some of which were exhibited) at least 8 inches by 9 inches. It will create, therefore, the less surprise, when it is stated that the section was not less, by our estimation, than 18 inches in diameter. It was sent by Mr. Lambert. Mr. Hemming forwarded some photogenic drawings, with the engravings from which they were copied; but neither these specimens, nor those exhibited on a former occassion by Mr. Talbot, and which Sir Anthony Carlisle has by an oversight attributed. in No. 809, to M. Daguerre, are not worth for a moment the attention of the artist, for, besides other defects, the lights and shades are reversed. Still the subject is curious, and to a trifling extent may be useful even at the present stage of its progress, where however it will not stop. The French, indeed, can show something more deserving of notice than these specimens, and what we conceive is totally different, both in the effect produced and in the process itself, except so far as the light of the sun is concerned.

The Lecture.-Mr. Brayley's subject was "The equilibrium of the atmosphere, as dependant on the united action of gravity and temperature." The purport of this lecture was the introduction of some speculations concerning the mechanical constitution of the atmosphere. The Lecturer first imparted the usual information respecting its weight, its elasticity, the law of its pressure and density, its sensible height, as determined by different methods, and the opinions which have been held at various times as to its limits, until they pretty generally accorded with that inferred from the researches of Dr. Wollaston, of its being impossible that the rarity of the air can exceed that point at which the repulsive force between its particles becomes less than the force of gravitation. He then adverted to

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M. Poisson's hypothesis, according to which, the limit of the atmosphere, instead of thus being one of almost insensible gradation, is abrupt and well-defined, through a process in the upper regions of the air, no less singular than that of its conversion by cold into a liquid or even a solid. Without taking this extreme view of the subject, nor yet controverting it, the Lecturer contended that, admitting that extra mundane space to be colder than the mean temperature of the air, it must follow that, at a certain point in the rarity, or in the height of the atmosphere, an inverse order of its density commences; so that beyond the region of greatest rarity (greatest under the supposed conditions), another region exists, in which the density increases in some ratio with the altitude, but whether it terminates in the liquidity of the air, it was no part of his inquiry to determine.

But

He attributed this effect to the extreme cold which is supposed to reign in space, and advanced in confirmation of his views, the singular vaccillating appearance which is observed in the progress of the oscultation of fixed stars by the moon; that is, supposing the moon to have an atmosphere, and that it is similarly constituted. what the Lecturer depended on principally for argument and illustration, is the remarkable deficiency of luminosity in a middle region of the atmosphere of comets, and which he had the authority of Sir John Herschell to attribute to the dissipation of its vapours by heat, and the luminous appearance of the outer region or coma, to the condensation of those vapours in an exterior sphere of greater cold. This he imagined to be a case in point, or analogous at least to his supposed constitution of the earth's atmosphere, the different nature of the æirial fluids being matter of no consequence. The only experimental illustration of his theory that he advanced, was the condensation of the attenuated vapour in Dr. Wollaston's cryophorous by the application of cold. This he gave as an instance of gradation in density, of a column of vapour as it approached the source of cold and became converted into water; and adduced the fact of liquefaction of the vapour, as a proof, as we understood him, of the high degree of density of the immediately previous and proximate state of the vapour.

Remarks.-M. Poisson, like a true mathematician, supports his hypothesis of the liquid state of the air at the extreme limit of the atmosphere, by a mere analytic investigation, resting on assumed atomic and other data, particularly that of the extreme cold existing in universal space-but which by the way is opposed to the deductions of M. Fourrier, also mathematically derived→→

means

and not only does he thus support it, without any reference to physical considerations and probabilities, and the recognised methods of legitimate induction, but in direct opposition to phenomena, particularly those which belong to optics. But Mr. Brayley, in behalf of his modification of, or rather addition to, Poisson's theory, argued the point on better grounds, and we will add in a more philosophical manner, by taking the principles and appearances appertaining to natural philosophy for his guide, though we greatly fear that they will by no bear him out in his views. We have, however just given him credit, in one particular, for more than he really performed; he having strangely omitted the argument, and advanced only the evidence he was able to collect for the inference from it, that cold produces an increasing density in the upper regions of the atmosphere. We must also say, that of one portion of this evidence relating to the occultation of stars, it cannot be allowed him, if what astronomers inform us be true, that the singular appearance attending it, is not common to all the stars. And in regard to the supposed constitution of the atmospheres of comets, it scarcely amounts to analogical evidence, for their vapours are imagined to be condensed in the sense of incipient liquefaction by the operation of cold, and not brought into a state of greater density as an elastic fluid. The nature of the phenomenon, if it be such as Sir John Herschell supposes, is corroborative rather of Poisson's than of Mr. Brayley's theory, allowing only for that immense distance of separation between the particles of condensed vapour, which its extreme tenuity denotes, and which prevents the formation of anything more approaching to a liquid than a fog. But Mr. Brayley may say that a state of greater density in the elastic fluid must necessarily precede its condensation into liquescent or visible vapour. However this may be, the appearance alluded to as belonging to comets, gives evidence only in, favour of the former fact, although it must have been in reference to the latter that Mr. Brayley could be supposed to have cited it. But what proof is there of the necessity just referred to? Does Mr. Brayley think the fact to be so established by the experiment with the cryophorous as to allow him to dispense with argument? It is scarcely necessary to say, and certainly it is not necessary to prove, that his statement of a difference in the density of the vapour in this instrument, being produced in proportion to its proximity to the source of cold, is by no means correct. The formation of water, to

which he pointed in proof of his assertion, was an inapposite fact, for the vapour was already of the greatest density consistent with its temperature, and on the application of cold, it collapsed at once into the state of water, without passing through any intermediate stages of density. Of course variations can be effected in the density of aqueous vapour, as well as in gases, and simply by the operation of difference of temperature, but it must be under other circumstances than those which were given. Cold, although spoken of in positive terms that are too apt to mislead, is not a positive but a negative cause, and cannot of itself produce an increase of density in air or vapour. It is an abstraction, or it is a diminution of repulsive force, but there the matter ends and the particles will remain as distinctly separate as before, unless there is an approximating force present, or elicited, to take advantage of the circumstance. Bu our limits are exceeded-still we must find room to say, that the lecture was very well got up.

NOTES AND NOTICES.

Launch of the Steamer Nicholai.-The ceremony of launching a splendid steam-vessel, named the Nicholai, took place on Saturday, from Gordon's Dock-yard, Deptford. She is the largest steamer belonging to Russia, and is intended to ply as a packet between Lubeck and St. Petersburgh. The Nicholai was built by Mr. Taylor, in the incredible short period of four months from the time of laying the keel, after the designs of Mr. Carr, of the firm of Ritherden and Carr, surveyors to the Hon.the East India Company. After being launched the vessel was immediately towed across the river to the establishment of Messrs. Seaward and Capel, of the Canal Iron Works, Limehouse, the firm to whom, by the special order of the Emperor, is entrusted the execution of the steam machinery. This machinery is to be precisely similar to that adopted on board her Majesty's steam-frigate the Gorgon, which has been so much approved of; and with a speed proportioned to that used in the construction of the wood work, the whole will be fitted up and the vessel entirely ready for sea in one month from the date of the launch. The engines will be of 240-horses' power, and the peculiar merits of the mode of construction adopted by the eminent engineers referred to are such that the machinery is greatly simplified, and the space which it occupies proportionably diminished. Thus the length of the engineroom in the Nicholai is only 45 feet, whereas on the ordinary plan it would exceed 62 feet. The advantage of having so much space in the most superior part of the vessel cannot be too highly estimated. This will be immediately evident form the fact that the Nicholai, of 800 tons burden, will carry 150 pas sengers-a number equal to that of the Great Western, of 1,400 tons. The success of the Gorg on, just returned from a six months' cruise on the coast of Spain, has been so pre-eminent that the Lords of the Admiralty have given orders for five more pair of engines on the same principle, to be fitted into five new frigates. One of these (the Cyclops) will be of 1,300 tons burden, with engines of 320 horses power. She will carry 20 guns, and be the largest man-of-war steamer in the world.