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meter during these days in 1843, that occasioned the general rise and fall, from the 11th to the 25th of November, 1842. At the request of the British Association, I undertook an examination of the symmet rical wave of November, 1842, which I commenced in September, 1843. One of the results of this examination has been to determine that the inflexions on the slopes of the large symmetrical curve are due to smaller waves, and that systems of these smaller waves are moving in various directions. The latest results of my researches relative to these secondary waves, are given in the notice of my report already alluded to [ante, No. 923.] These researches tend very much to establish the idea of a large normal wave, and render very probable that the wave observed in 1843 was the same as that observed in 1842, although the inflexions arising from waves of a secondary character were different.

The autumn of 1844 again brought us this interesting visitor. During the period, from October 21st to November 2nd, a rise and fall of the barometer occurred, in many respects similar to the two preceding the identity in this case was not so distinctly marked, but there was still sufficient symmetry in the ascending and descending branches of the curve to render it highly probable that the oscillation was due to the same cause that produced those in 1842 and 1843.

This great similarity in the barometric movements occurring about the same period in three consecutive years, induces a hope that this wave may again return; and meteorologists are invited to direct their especial attention to the oscillations of the barometer during the months of October and November next; should it return, we shall, by multiplying observations upon it, be in a much better position to examine it in every possible aspect, and by separating from the observations every circumstance that can at all influence the barometer, we shall be able to contemplate it entirely free from every cause that can at all influence it, and by which its form, direction, velocity, &c., may be modified.

In order to carry this out effectually, two or three considerations

are essential.

1st. It appears that the line joining Dublin and Munich is an axis or line of greatest symmetry; it is, therefore, desirable that numerous observations should be made on this line-Birmingham and Brussels are two important stations on it.

2nd. As nearly as possible stations should be chosen on each side this line, so that they may be arranged with a certain regard to symmetry. A much better idea of the wave could be obtained from observations made at stations equally disposed with respect to it than otherwise.

3rd. Those instruments should be observed contemporaneously with the barometer that are capable of giving us information by which we can obtain the true pressure of the gaseous atmosphere.

With this view, I have drawn up the following instructions, which I shall be most happy to forward to gentlemen desirous of taking part in these interesting observations, (upon being applied to for that pur

pose,) accompanied with printed forms for recording the observations. The instructions consist

1st. Of the times of observation.

2nd. Of the instruments to be observed.

3rd. Of the data necessary for reducing the observations, and rendering them suitable to be employed in this inquiry.

Times of Observation.-The following hours are the most suitable for the object now in view: 3 A. M., 9 A. M., 3 P. M. and 9 P. M.; these hours divide the day into four equal parts; they have been recommended by the Royal Society as meteorological hours, and are the hours at which observations are made daily, by direction and under the superintendence of the Honorable the Corporation of the Trinity House, which have been most advantageously used in the examination of atmospheric waves. In cases, however, in which the observation at 3 A. M. may be inconvenient or impracticable, it will be important to substitute for it two observations, one at midnight and the other at 6 in the morning, so that the hours of observation will in such cases be 6 A. M., 9 A. M., 3 P. M., 9 P. M. and midnight. To individuals who cannot command these hours, it is recommended that observations should be made as near them as possible; these will still be valuable, although not to so great an extent as those made at the regular hours. In these cases, however, it will be absolutely necessary to substitute two readings for every one of the regular hours omitted-one previous to, the other succeeding, the hour so omitted; and these should, if possible, include an equal interval both before and after such hour. In all cases the exact hour and minute of mean` time at the place of observation should be inserted in its appropriate column in the form for recording the observations.

Instruments to be observed. At the regular hours of observation, or any others that the observer may fix upon, in accordance with the foregoing instructions, it will be necessary to observe,-1st, The barometer, with its attached thermometer, and enter in the form the actual height observed, with the temperature of the mercury. 2nd, The external and dry thermometer. 3rd, The wet bulb thermometer. (These observations are particularly essential, in order to separate the pressure of the vapor from the aggregate pressure, as measured by the mercurial column.) 4th, The direction and force of the wind. (These are important to determine the connexion between the undulatory and molecular motion of the wave.) 5th, The character of the weather at the times of observation; which may be recorded by Capt. Beaufort's symbols. It is proposed to commence the observations on the 1st of October next, and continue them daily, until the end of November, unless it should be found that at that time the wave is not completed, in which case it will be requisite to continue them a few days longer.

Data for Reduction.-It will be necessary, on returning the form when filled, to accompany it with the following data for reduction. A blank is left for this purpose on the back of the form. The geographical co-ordinates of the place of observation, viz. latitude and longitude. The altitude of the cistern of the barometer above the

level of the sea, exactly, if not, as near as it can be obtained. The internal diameter of the tube of the barometer. The capacity, neutral point, and temperature. (These are usually engraved on the instrument.) If the co-efficients of the diurnal and annual oscillations have been determined for the place of observation, include them.

sets of observations which may be reduced by the observers should be accompanied with the original observations, and a reference to the tables used in their reduction, also the data above mentioned. All observations that may be made in accordance with these instructions and forwarded to me, will be carefully examined and reported on at the next meeting of the British Association.

N. B. Observations will be made at several light-houses, by direction of the Honorable the Corporation of the Trinity House, and Capt. Beaufort has kindly undertaken to obtain observations from several of our surveying vessels.

London Atheneum.

Extracts from the Proceedings of the Paris Academy of Science. APPARATUS FOR INDICATING DANGER FROM FIRE DAMP, OR ESCAPE OF GAS, by M. Chuart.-M. Chuart's invention consists of a ball or globe, contained in a chemical solution highly sensible to any deterioration of the atmosphere, and acting upon a lever, which sets an index in motion, and thus shows the vitiated state of the atmosphere, whether in a mine, or elsewhere, long before the common air can be so saturated with gas, as to explode on the application of a light. M. Chuart has added to his invention an alarum bell, which is struck by the lever when the ball is thrown off its equilibrium by the vitiated state of the atmosphere. Since M. Chuart first exhibited his apparatus he has made a great improvement. His ball was originally of glass, which was not only too heavy, but also liable to breakage. He now makes it of copper, so very thin that its weight is almost nominal, and yet it is perfect in every part. We understand that he arrived at this perfection by means of the galvanic process, which gives a thinner substance than any mechanical means could effect consistently with the compactness that is required for the certain operation of the appa

ratus.

ON THE RADIATION OF HEAT, by M. Melloni.-It is known from the experiments of Rumford and Leslie, that the surfaces of different bodies possess in very different degrees the faculty of giving out by radiation the heat of the substances which they envelope. It is also known that layers, more or less thick of the same varnish, or other covering of this kind, considerably modify the radiating power of the surfaces over which they are laid. This fact showed that the rays of heat given out by a substance proceeded not merely from the surface, but also from points under it, and at a certain depth. What remained to do was to measure numerically the thickness of the superficial layer which assists the radiation; this is what M. Melloni has undertaken. He covered the faces of Leslie's cube with equal layers of a proper varnish, augmenting successively the number of layers, and

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measuring each time with his thermometrical apparatus the radiating powers of the surfaces. He found that the power went on gradually increasing up to the seventeenth layer of this varnish, when it became stationary. At this time, the total thickness of the varnish, as ascertained with all possible minuteness, was about four hundredth parts of a millimètre (as the millimètre itself is only the thousandth part of about three feet, M. Melloni must have had great difficulty in coming to this minute calculation.) In comparing the preceding results with those which attend the use of leaf gold, M. Melloni found that a much thinner coating of gold (viz. two thousandth parts of a millimètre) would produce the same amount of radiation. M. Melloni shows that this difference is not to be imputed to the greater or lesser transparency of the coating, for lamp black, which is very opaque, possesses, like varnish, the property of giving out the rays of heat from the layers on which it is placed.

ON POISONING BY METALS.-Messrs. Danger and Flandrin presented a final paper upon poisoning by metals. The metal particularly noticed in this paper is mercury. Hitherto it has been difficult to detect the presence of mercury in organic matter when administered in some of its combinations. Messrs. Danger and Flandrin have succeeded in the means of discovering even the hundred-thousandth part of a grain. Their analytical process, after carbonization with sulphuric acid greatly modified, is with the galvanic pile of Smithson, with a certain modification, by which the gold conductors plunge in the suspected liquor and separate the mercury.

ATMOSPHERIC RAILWAY, proposed by M. Arnollet.-A report was read by M. Lainé on a system of atmospheric railroad proposed by M. Arnollet. In the system of Mr. Clegg it is necessary, in order to expel the air from the directing tube, to employ a powerful steam engine, the action of which is interrupted during the time that elapses between the arrival of one train and the departure of another. To prevent the loss occasioned by this intermittence, M. Arnollet proposes to employ a smaller engine for the constant exhaustion of one or more grand reservoirs, to be put in communication with the tube during the motion of the trains. No experiment on a sufficiently large scale having been made to test this modification, the Committee appointed to report has given no positive opinion. Judging, however, from the elements of M. Arnollet's theory, the committee thinks it possesses certain advantages which render it worth an experimental trial.

CHEMICAL EQUIVALENTS.-M. Pélouze presented his new table of the equivalents of most of the simple bodies in chemistry, as compared with the table of Berzelius. It results from the conclusions of M. Pélouze, that azote, phosphorus, and arsenic, are the only bodies with carbon, the equivalents of which are exactly divisible by 12.5, the equivalent of hydrogen, and that, consequently, we cannot give to the law of Dr. Prout, by which the equivalents of all bodies are exact multiples of that of hydrogen, the general character which M. Dumas

supposes.

WHIRLWIND NEAR ROUEN, AUGUST 19TH, 1845.-M. Arago gave, from letters which he had received, an accurate account of the whit wind, which, on the 19th inst., caused so much disaster near Rouen M. Precisier states that the blast, or whirlwind, in question had its origin at Houlme, a village two leagues from Rouen. Two violent winds proceeding in contrary directions having met, a cone was formed, which descended from the clouds, with its summit towards the earth, and had a revolving motion of terrible rapidity. From its centre issued flashes of lightning, and it emitted a strong smell of suiphur. Some persons, who saw it advance with enormous speed, have assured M. Precisier that the black and red clouds moved vertically, driven backwards and forwards with prodigious force; they also heard a rolling noise, similar to that which precedes hail. The barometer fell suddenly from 29.786 in. to 29.156 in., the temperature of the air became much elevated, and the whirlwind was preceded by a current of air so warm that some persons before a large fire felt it strongly. The meteor rushed eastward, overthrowing everything it met with in its course; it passed through a forest without losing any of its power, -snapping off or twisting the trees, and casting them right and leftand then struck a cotton factory four stories in height, and in a second demolished it, crushing the persons who were within its walls. The dwelling-houses which were in the immediate vicinity of this factory were but slightly injured; for the whirlwind did not take a direct course, but went in zig-zag, and appeared to be attracted by the great masses of iron in the machinery of the factories. At the second factory that it attacked, the third floor was swept away in an instant, and some of the fragments were carried to a distance of several leagues. The third factory, in which there were nearly 200 persons at work, was demolished with the same rapidity as the other two. The meteor then continued its course towards Malaunay, devastating the country as it proceeded; but at Clèves its effect ceased. A violent wind, caused by this frightful perturbation at one point, blew from it towards all the environs, and was felt at a great distance. At La Chapelle, near Dieppe, a distance of nine leagues, a shepherd saw fall a plank of more than a metre in length; slates, portions of windows, cotton, and many other objects fell near the same spot. All the facts which were witnessed, says M. Precisier, prove the presence of electricity in this visitation. The bricks and stones of the buildings which were destroyed were burning hot, and many articles were carbonized on the outside. Some spindles were found to be magnetized; but M. Arago observed that this might have been the case before the disaster. The bodies of the victims presented no marks of external injury; they resembled those of persons struck by lightning. As to the light which was seen to issue from the centre of the meteor, no doubt of its being electric can be entertained, and it was visible at a great distance. In the neighborhood of the disaster, a family, who were about to sit down to dinner, suddenly saw the table uncovered; the plates and dishes danced in the air, and a frying-pan was driven. upwards, and forced into the ceiling, surrounded by a light which rapidly disappeared.

London A henæum.

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