the fumes of muriatic acid gas which they evolve during their decomposition by strong sulphuric acid. On bringing a stopper or glass rod moistened with ammonia in contact with these fumes, dense white clouds of muriate of ammonia are produced.

Before the blowpipe the chlorides may be known by melting oxide of copper and microscomic salt into a green bead; to this the assay is to be added, and the presence of muriatic acid will be shown by the blueishpurple flame with which the globule will be surrounded on again exposing it to the blast.

CARBONIC ACID.

THE carbonates are easily distinguished by being decomposed with effervescence from the disengagement of an inodorous gas (which is carbonic acid gas), when treated either in the dry state, or in solution with almost all the acids.

PHOSPHORIC ACID.

ALL the neutral phosphates, except those of the alkalies, are only sparingly soluble in water, but dissolve in an excess of phosphoric acid and in nitric acid.

The insoluble phosphates (of which those of lime, baryta, and lead are the most so,) may be dissolved by boiling them with a strong solution of a carbonated alkali. Phosphoric acid is not easily detected by the humid process. Precipitates are caused in solutions of the neutral phosphates of the alkalies by chloride of barium, chloride of calcium, lime-water, and water of baryta, and the precipitated phosphates are soluble in nitric and muriatic acid; but these precipitates are not easily distinguished from the precipitates formed by the above reagents with some other acids, and therefore the presence of phosphoric acid is not proved until the absence of those acids has been determined by other .experiments.

Acetate, or nitrate of lead, also forms, with phosphoric acid, a white precipitate insoluble in acetic, soluble in nitric acid. The precipitated phosphate of lead, when fused in the outer flame of the blowpipe on charcoal, crystallizes as it cools, a property peculiar to the compound of phosphoric acid with lead.

Nitrate of silver produces in solutions of neutral phosphates of the alkalies, a yellow precipitate, soluble in nitric acid and in ammonia; and as all the acids which resemble phosphoric acid (except the arsenic) cause, with oxide of silver, precipitates of a different colour from this, nitrate of silver is one of the best tests of phosphoric acid in solution.

There is, however, but one property characteristic of phosphoric acid, and phosphoric acid alone, which is, that when combined with protoxide of lead, it forms a salt which, on being fused by the blowpipe, crystallizes as it cools.

BORACIC ACID.

BORACIC acid is distinguished by the green colour which it communicates to the flame of burning alcohol. The borate, reduced to powder, is to be moistened with sulphuric acid, and covered with alcohol, which is then

inflamed. No chloride must be present, as the chlorides impart to the flame of burning alcohol a greenish colour, though of a somewhat bluer tinge than that produced by boracic acid.

HYDROFLUORIC ACID AND FLUORIDES.

THIS acid is easily recognised by its peculiar property of corroding glass. Solid fluorides are to be reduced to powder, and mixed with concentrated sulphuric acid in a platinum crucible. This is to be covered with a plate of glass, previously coated with wax, through which letters have been scratched, and, on cautiously heating the crucible, so as not to melt the wax, the glass will be found deeply corroded in those parts which are exposed to the action of the fumes of the hydrofluoric acid generated during the process. The same effect is produced on glass by solutions of the fluorides (if not too dilute) when mixed with sulphuric acid.

METEOROLOGY.

Seven Lectures on Meteorology.-By LUKE HOWARD, Gent., F.R.S., &c. Pontefract, J. Lucas.

THE author of this little work is celebrated among meteorologists for his classification and nomenclature of clouds, the merit of which is proved by its general adoption among all who cultivate the science; and there are few writers on the subject more often cited for accurate observations, and for data connected with atmospheric phenomena. A work, therefore, from Mr. Howard, on the subject of Meteorology, would naturally excite interest by its appearance, and we are gratified in finding that the volume before us will uphold the author's reputation. These Lectures contain a clear, familiar, and scientific explanation of the principles of Meteorology, and, to render the work useful as a text-book to lecturers and teachers, there are notes appended, containing instructions for making the experiments necessary to elucidate the subject, and descriptions of the apparatus that would be required. That, however, which constitutes the recommendation of the book, its popular nature, precludes our finding much to comment on, to readers who possess more than the most elementary knowledge of the subject. We remark, however, in turning over the pages, that Mr. Howard still adheres to certain hypotheses which have been given up by later meteorologists; as, for example, that meteoric masses, which fall to the earth, are the results of the combustion of gases produced from the earth's surface.

"Certain it is, however, and ascertained on the most satisfactory evidence, that some of these bodies have let fall not merely single stones, but a whole shower of these, on the tracts over which they have passed: and the composition of such bodies, collected from various countries, as found by chemical analysis, has confirmed the opinion that they have all one common origin. Now, though some philosophers have preferred to make, even of the smaller meteors, very distant bodies, extraneous to our atmosphere; and have

brought the larger from the moon in the form of projectiles, there is very strong ground to presume that the white trains which falling-stars leave behind them (at some seasons and not at others), are in reality the ashes of the combustion of a mixed inflammable substance, chiefly gaseous; which residue, at first incandescent, gradually vanishes by cooling where it is left, and subsides unperceived through the air. Again, that the solid stones, which have the appearance of earthy concretions, suddenly formed in a heated medium and glazed by flame on the surface, are the cinders and slag of a still larger aërial fire; of a furnace, indeed, (for such was the aspect of the meteor of 1783), carried through the air with the apparent falling of burning coals from it, which become extinct in their descent.

"The composition of these Meteorolites, their history, and probable origin in vapours, carried up from the earth and fired aloft, would form of themselves a very interesting lecture, but which does not enter into the plan of my course. Suffice it to say, that though the stones in question have been ascertained to have fallen from the heavens by day, in various parts of the world, and from remote antiquity-it was not so easy (and yet modern observation has been found equal to this,) to prove their connexion with the bolis, moving through the air, and drawing flame behind it. This, however, being proved, with the fact that hydrogen gas is capable of dissolving various bodies, even iron and that it is naturally evolved, mixed with carbon in the gaseous state, in very large quantities (even from every piece of stagnant water, in the autumnal season,) we have a right to presume that, on occasion, it is collected in vast fields, to be fired by electric explosions, or by some play of affinities in nature, of which we have not, as yet, a proper conception; and (the gases burning out) to let fall the earthly and metallic contents, precipitated and agglutinated as we find them in the aërolite. A meteor of such a nature, covering an extent of many acres in the atmosphere (as these do), may very well afford a brilliant light, and (though but slightly charged in proportion to the mass with solid matter) also the residue of the combustion, which descends. But a body of the size of the largest aërolite, coming solid from space into our atmosphere (admitting it to take fire on first entering), would form but an inconspicuous object in its descent."

We entertain great respect for Mr. Howard's talents as an observer and as a meteorologist, but we confess we are puzzled at his chemical tenets. Can he inform us of any proven instance of iron being held in solution by hydrogen, or by any gas? or being combined in any appre ciable quantity with an aëriform substance without destroying its fluidity and gaseous properties? Mr. Howard leaves the strong point of the opposite argument untouched-the alloy of iron and nickel, invariably found in meteoric masses, and never, as yet, in terrestrial minerals. He also seems totally to reject the collected evidence on the periodical reappearance of asteroïds, bearing so strongly on this point, and the vague hypothesis adopted by him, can in no way account for the horizontal motion through our atmosphere of the meteoric masses alluded to.

As regards Meteorology, we are now arrived at that point in our progress at which all further advance is hopeless, till a vast mass of accurate and extensive observations is collected, to serve as material for working out some expressions for the complicated laws governing atmospheric phenomena. Unfortunately, to collect such observations requires considerable skill and patience, and presents little to incite those qualified for the task to undertake it. The astronomer, in multiplying observations

connected with his pursuit, has the certain pleasure to look forward to, of finding the most striking confirmations of established laws from every such exertion, and the exquisite intellectual gratification of applying the most refined and beautiful analysis to work out the results, while the grandeur of the scenes he contemplates, and the lively hope of possibly becoming the discoverer of some unknown planet, some new nebula, or binary star, stimulates and cheers him in his task. So the naturalist, the geologist, the botanist, and other cultivators of science, find incentives without end to the prosecution of their researches, but registering hourly fluctuations of the barometer, thermometer, and experimenting with hygrometers, or rain-gauges, is but a tedious task, and can hold out no other premium but the consciousness of being usefully employed. Now it can hardly be expected that those competent to this task will undertake it, unless they derive some recompense that will induce them to waive their pretensions to any celebrity to which they might attain by other pursuits. It therefore belongs to scientific bodies, or more properly still, to governments, to establish well-endowed institutions for making continuous and accurate observations at several distant stations throughout their respective countries. Till this has been done without intermission for several years together, Meteorology must remain as it now is, a science of plausible hypothesis, instead of laws relating to natural phenomena, strictly founded by induction on accurate observations of facts.

ON THE STEAM-ENGINE.

By M. ARAGO.

[Continued from page 20.]

1705. NEWCOMEN, CAWLEY, and SAVERY*.

THE draining-engine, known among engineers by the name of Newcomen's, or the atmospheric engine, was the first which rendered any essential service to the useful arts.

I may say that even in a great number of situations where fuel is not expensive, it is still in use, and no inducement has yet been found to substitute any other for it. Further, this engine, except in some important details in the construction which I shall point out as we proceed, is no other than the engine proposed in 1690 and 1695 by Papin, and which he had attempted on a small scale.

In fact, in one, the same as in the other, may be remarked a cylinder, or vertical metallic pump-barrel, closed at bottom, open at top, and a piston properly adapted and intended to traverse the whole length.

Thomas Newcomen and John Cawley cretary of the Royal Society, one of the were both inhabitants of the town of Dart- most ingenious savans that England can mouth, in Devonshire. In the English boast of. It is not known whether the two biographies of the first, he is sometimes partners took an equal share in the expericalled an ironmonger, sometimes a black-ments of various kinds which led to the smith. The other was a glazier. Newco- construction of the first large atmospheric men was a man of some information, and engine.

a literary correspondent of Hooke, the Se

In one, as in the other, the up-stroke of the piston is effected by a counterpoise, and the aqueous vapour then enters freely into the lower part of the cylinder and fills it. In the English engine, as in that of Papin, as soon as the up-stroke of the piston has terminated, and the vapour which had forced it has become condensed, a vacuum is produced throughout the whole of the space which the piston had passed through, and the atmosphere then causes it to descend. Papin announced that the condensation must be produced by cold; and it was by cold that Newcomen, Cawley, and Savery, got rid of the vapour which counterbalanced the atmospheric pressure. Among several different contrivances that might be imagined to do this, (these are the expressions contained in the Recueil de Pièces, p, 53,) the English mechanicians have adopted one, far preferable in a large engine to that which Papin himself employed in the experiments made with his small model. Instead of removing the fire, as was done in the latter, Newcomen, Cawley, and Savery, threw a copious quantity of cold water into the annular space comprised between the exterior sides of the cylinder and a second cylinder rather larger, which served as an envelope. The refrigeration was thus gradually transmitted through the whole thickness of the metal, and in a short time reached the vapour itself.

Papin's engine, thus modified as to the process of cooling the aqueous vapour, excited the attention of mining proprietors to the highest pitch, and appeared, from the first, to furnish an unexpected solution of a problem, the difficulty of which had been remarkably exhibited by the fruitless trials of Savery.

Newcomen and Cawley solicited a patent, but Savery objected to it, as he was already in possession of an exclusive privilege for the production of a vacuum by the refrigeration of vapour. In order to avoid all dispute, the patent was taken out in the names and for the profit of the three competitors, who thus assumed to themselves a project borrowed from Papin, the two first taking the idea of the piston steam-engine, the third that of condensation *.

In the arts, as in the sciences, the last | to construct.-(See ROBISON; A System, comer is supposed to be cognizant of the &c., vol. ii. p. 58.)1 works of his predecessors; all denial, every declaration to the contrary, is of no weight. The publication of the Memoirs written by Papin upon the atmospheric engine, being greatly anterior to the patents of Savery and of Newcomen, I could have no motive for examining whether the English engine is, or is not, a copy; according to the rule, it is a copy, because it resembles the engine of Papin, and because it came after it; but, in this particular case, it is further known that Newcomen was acquainted with the projects of our countryman. It is proved, in fact, by several notes found among the papers of Hooke, that the Dartmouth engineer had consulted this celebrated savant before undertaking his experiments, and also that, in the confidence of friendship, he admitted that it was really the French engine he intended

["Newcomen was a person of some reading, and was in particular acquainted with the person, writings, and projects of his countryman Dr. Hooke. There are to be found among Hooke's papers, in the possession of the Royal Society, some notes of observations, for the use of Newcomen his countryman, on Papin's boasted method of transmitting to a great distance the action of a mill by means of pipes. Papin's project was to employ the mill to work two air-pumps of great diameter; the cylinders of these pumps were to communicate by means of pipes, with equal cylinders furnished with pistons, in the neighbourhood of a distant mine; these pistons were to be connected by means of levers with the piston-rods of the mine. Therefore, when the piston of the air-pump at the mill was