ceptions, turned inwards on both sides towards the centre of the track; while near the centre, the direction of the prostrate bodies is coincident with that of the storm."

Professor Forshay in his account of the Natchez tornado is equally in point. He declares that "the nearer the axis of the tornado, the nearer were their bearings parallel with that axis, and the more remote, the nearer perpendicular, while those that point to the direction from which the storm came, or cross a line perpendicular to the axis, lie beneath those that point in the forward direction of the same.'

We may mention also, that the storm which occurred in France, of which we have given a chart in the former part of this article, could not possibly have been of the whirlwind character. Had the wind moved in a whirl, the hail which fell during its progress, must have been scattered over the whole area of the storm, and not been deposited in two veins for many miles as we have seen. If the whirlwind theory is correct, therefore, this storm at least must have been a wonderful exception to the general law.

But Mr. Espy does not rely alone on the direction of fallen trees in tornadoes to prove the centripetal course of the wind in storms. By means of observers in different sections, he has been enabled to surround some of our great northern storms, and has satisfied himself that the same law uniformly prevails. We can only make a few selections from the great number which we find recorded in the volume before us.

The following diagram represents a destructive storm which swept along our southern coast in the middle of August, 1837. The facts respecting it were collected by Col. Reid, but Mr. Espy finds that they maintain his own views, although recorded by an advocate of the whirlwind theory. The map represents the position of the storm as it was at noon, on the 18th of August, and the arrows are intended to show the direction of the wind at that time.

Mr. Espy observes: "I have culled out of this storm, that portion of time in which I find the greatest number of simultaneous observations, and I have exhibited on the annexed wood-cut the localities of all the ships within the boundaries of the storm, whose latitudes and longitudes could be ascertained with any degree of certainty, with arrows, exhibiting the

course of the wind. The time is noon of the 18th of August, 1837. At this time, the Duke of Manchester was only a few miles N. E. of the centre of this storm; for some time in the afternoon, the centre of the storm passed nearly over her, when the wind changed pretty suddenly S. W. At this time, and for some seven or eight hours both before and after, all those ships which were laboring in the most violent part of the storm, had the wind blowing towards a central space of no great magnitude. This settles the question of a violent centripetal motion of the wind in this storm, in conformity with the five previously examined, and also with the twelve investigated by the Joint Committee of the American Philosophical Society and Franklin Institute, and with not less than fourteen land-spouts which have already been examined, in all of which the trees were thrown with their tops inwards--and when any are thrown across each other, those which are underneath, are uniformly found to be thrown inwards and backwards, and those on the top, to be thrown inwards and forwards, just as they should be, if the wind blows inwards. Whereas, if the wind is centrifugal, many of the trees should have the tops thrown outwards on both sides of the path."

The following chart represents the course of the wind in the storm which occurred in Great Britain on the 17th of August, 1840.

0. Workington, changed at 10, A. M., from S. S. E. to N. N. W.-1. Plymouth, W. on 17th, S. W. on 16th.-2. Pill-Bristol, S. W., A. M.3. London, southwardly, on 17th. 4. Lynn, heavy S. till noon, then S. W., more mod. erate.-5. Hull, S. S. W., strong.-6. Leeds, S. E. or S. S. E., strong from 8, A. M., to 1, P. M., clouds at this time moving from S. W.-7. Sheffield, S. S. E. all day, next day, E. Strong on 17th.

8. Hyde, near Manchester, S. W., in the morning; west in P. M.; strong gale all day. -9. Liverpool, S. W., A. M., N. Westerly, P. M., strong.10. Belfast, N. by W. strong gale.-11. Point of Ayre Light, N. W. gale.-12.

Corsewell Light, N. N. W., storm.-13. Dublin, W. N. W.-14. Largs, heavy from N. N. W. from 7, A. M. till 8, P. M.-15. Kyntire Light, N. W. gale.-16. Pladda Light, N. W. breeze.-17. Greenock, N. W. and N.-18. Lismore Light, N. W. gale.-19. Dumferline, N. and N. E. till 2, P. M. increasing to a gale.-20. Edinburgh, N. N. E. strong. -21. Berwick, S. by E. to S. E., strong.-22. Aberdeen, E. all day, strong.-23. Middle line of the storm on morning of 17th.

To the mariner it is of immense importance to discover the true law of storms. As his life and property will often depend upon the theory which

he has adopted, and which governs him in the control of his vessel when the element on which he sails is in dread commotion. If the course which storms pursue may be known, and it be true that the wind drives in on all sides towards a common centre, the seaman has an unerring guide for his conduct, which, if generally known, must greatly tend to the preservation of property and life. We have been informed by an American, who was present at Mr. Espy's lectures in Liverpool, that a gentleman of high standing, in his admiration of the very beautiful theory which the lecturer had been expounding, took occasion to observe, that if the masters of vessels which sailed from Liverpool on the memorable 6th of Jan., 1839, had known what Mr. Espy had clearly taught them that night, not one of them would have been lost, for they would not have put to sea in the face of such formidable indications of a storm. This observation will serve to show the importance of the subject to all who traverse the ocean.

It is known, that Mr. Espy himself has the greatest faith in the theory which he has put forth, and on several occasions has predicted the approach of a storm, and published his predictions in the papers before the storm appeared. If the doctrines which he teaches are true, this becomes a very simple matter. The barometer which falls in the centre of the storm, rises all around its borders and particularly before it, because as the cloud swells out at its sides, it presses together the surrounding atmosphere and thus increases its weight. The rise of the barometer then will indicate the presence of a storm in some region at no great distance, and if the wind at the same time sets in towards the point from which storms are known to come, it will scarcely be possible to mistake the result.

We are gratified to see that Mr. Espy's views have attracted much attention among the scientific men of the old world. The French Academy have given his theory the fullest sanction, and we cannot resist the temptation to place their report upon our pages.

Report of the Academy of Sciences, (Paris,) on the labors of J. P. ESPY, concerning Tornadoes, &c.

Committee, Messrs. Arago, Pouillet, Babinet reporter.

"Messrs. Arago, Pouillet, and myself, have been appointed by the Academy to make a report to it upon the observations and theory of Mr. Espy, which have for their object the aerial meteors known by the names of storms, water-spouts and tornadoes, which cause so much destruction on land and sea in the vicinity of the Gulf of Mexico. These storms are produced in the same manner in every part of the globe, when a few given circumstances concur in one place.

"The labors of Mr. Espy have already considerably occupied the attention of the learned world, and may be considered under three different points of view. First, the facts which he has recognised and substantiated, and the proofs which support them; second, the physical theory, by which he explains them, and the conclusions which he deduces from that theory; third, the observations which are yet to be made according to this theory, based upon facts, and the practical rules which the mariner, the farmer, and the meteorologist will obtain from it; the two former for their own benefit, the latter for science, which is useful to all.

"The facts which result from the numerous documents which Mr. Espy has placed in the hands of the committee, are the following: the motion of the air in the meteor under consideration, called tornado or water-spout, if it is violent, and of small extent; a storm, if it covers many degrees of the earth's surface; the motion of the air, we say, is always convergent, either towards a single centre, when the tornado has a circular form and limited extent, or towards a diametrical line, when the tornado or storm is of a lengthened form, and extends over many hundred leagues.

"If the tornado is very small, in which case the violence of the motion of the air is greater, a cloud is frequently seen in the centre, whose point descends more and more until it touches the earth or sea. Water-spouts are small tornadoes, and the force of

these meteors in the south and east of the United States is such, that trees are carried up in the air, and the heaviest objects are overturned, displaced, and transported. Finally, we have only to call to mind the well known storms of the Antilles, which change even the form of the ground over which they pass. We will adopt the technical word tornado to designate the meteor in question, whatever may be its extent or violence. China and the neighboring seas, Central Africa, and the southwest part of the Indian Ocean, are, like the West Indies, the theatre of meteors of the same nature, and not less disastrous.

"In observing at the same moment the force and direction of the wind, which is shown by the overturned trees, the displaced movable objects, in a word, by the traces impressed upon the soil, Mr. Espy proves that in the same instant the motion of all parts of the air which is reached by the tornado is tending towards a central space, point, or line, so that if the wind on one side of the meteor blows towards the east, it blows with the same violence towards the west on the other side of the tornado, and frequently at a very short distance from the first place, whilst in the centre an ascending current is formed of astonishing rapidity, which, after having risen to a prodigious height, spreads out on every side to a certain limit, which we shall soon determine by the observations of the barometer. This ascending current loses its transparency at a certain height, and becomes a true cloud of the kind called cumulus, the base of which is horizontal, and whose height is determined by the temperature and humidity of the atmosphere. The central cloud of the tornado is constantly reproduced, in proportion as it is carried off by the rapid current of the centre; and, according to Mr. Espy, when rain or hail proceeds from this meteor, which is generally the case, it is the cold, caused by the ex. pansion of the air carried into the higher regions of the atmosphere, which condenses the water. Electricity, when it appears in the tornado, is not, according to Mr. Espy, essential to the phenomenon.

"The existence of an ascending current of extreme violence once placed beyond doubt by the phenomena of the rising of the air, and its motion towards a centre or towards the great diameter of the oblong space occupied by the tornado, being well established by facts, Mr. Espy examines the progressive movement of the whole meteor, which is very slow, compared with the velocity of the wind in the mass of air which becomes at each instant a part of the tornado. Mr. Espy shows that near the latitude of Philadelphia, where cirrus clouds, very elevated as is known, move towards the east, the centre of the tornado moves almost always towards the east, as well as in Europe, where the west wind is predominant; whilst, in the inter-tropical regions, (Barbadoes, Jamaica, the north of the Indian Ocean,) the meteor moves towards the west or north. west, following the course of the trade winds. These assertions are also verified with regard to China and the Indian Ocean, according to the maps of Berghous. The ba rometer, in the centre of the meteor, is sometimes nearly 2.25 of an inch (sixty millimetres) lower than towards its border, and its limit is marked on all its outline by a closed curve, along which the barometer is found to be at its "normale" height, whilst, on the other side of this line, further from the centre, the barometer is observed to rise, which rise in small tornadoes is .08 of an inch, (two millimetres,) but which may be forty or forty-eight hundredths of an inch, (ten or twelve millimetres,) in very extended storms. If the centre of the tornado moves, (which may take place in any direction, when compared with the diametrical line,) and the effects produced by the motion are examined, it is always found that if the meteor has followed in its motion the line of its greatest diameter, the tree which fell the first, indicates a point anterior in the path of the meteor, and the tree which fell last, a posterior point. Thus it is constantly found that the trees which were overthrown with their tops turned towards positions anterior to the centre of the tornado, are covered by trees falling in the direction of the centre at a posterior period. In short, in this same case, the branches of the trees not overthrown, growing on the side farthest from the opposite side of the line which the centre of the meteor takes, have followed the wind, and are twisted around the trunk of the trees. "The circumstances favorable to the sudden production of a tornado, large or small, are, according to Mr. Espy, a warm and humid atmosphere, covering a country suffi. ciently level and extended, still enough to allow that part of the air which is accidentally the least dense, to rise to a great perpendicular height above the middle of the heated space which is charged with transparent vapor; moreover, in the higher regions, a cold and dry air, whose situation and especially whose density contrasts with that of the as cending current which dilates, cools, loses its transparency by the precipitation of its dampness, keeping notwithstanding a specific gravity less than that of the air which surrounds it, and by its expansion presenting the form of a mushroom or the head of a pine

with or without the prolongation or appendage towards the base, which appendage, cloudy and opaque, shows a space where the expansion and the cold are at their maximum, and where, consequently, the precipitation of vapor commences almost immediately above the ground or the surface of the sea.

"Such are then the principal points which Mr. Espy has obtained from numerous observations. The motion of the air towards the centre of the meteor, the depression of the barometer in the centre, the central ascending current, the formation of cloud at a certain height, and its circular expansion after this cloud has attained a prodigious height, an expansion accompanied with rain and hail, and finally, the motion of the whole me. teor, en masse; these, I say, are the points which the extensive labors of Mr. Espy, his own observations, and the documents which he has collected, and which he intends publishing immediately in a special work, have placed beyond doubt, and which seem even to have triumphed over every objection, and to have rallied all opinions to his own.

"Let us now see the theory upon which he bases his observations, or rather which is based upon these facts well observed, well proven, and always reproduced in nature with similar circumstances.

"Mr. Espy thinks that if a very extended stratum of warm and humid air at rest, covers the surface of a region of land or sea, and that by any cause whatever, for example a less local density, an ascending current is formed in this mass of humid air, the ascending force, instead of diminishing in consequence of the elevation of the rising column, will increase with the height of the column, exactly as though a current of hydrogen was rising through the common air, which current would be pushed towards the top of the atmosphere, with a force and velocity in proportion to its height. This column of heated air may also be compared to that in chimneys and stove-pipes, of which the draught is in proportion to the height of the pipe containing the warm air. What then is the cause which renders the warm and humid ascending current, lighter in each of its parts than the air which is found at the same height with these different portions of the ascending column?

"This cause, according to the sufficiently exact calculations [tres suffisament exact] of Mr. Espy, is the constantly higher temperature which the ascending column retains, and which proceeds from the heat furnished by the partial condensation of the vapor mixed with the air, making this ascending column a true column of heated air, that is to say, of a lighter gas; for the weight of the water which passes into the liquid state, is far from compensating the excess of levity which proceeds from the more elevated temperature which the air preserves. (This weight only equals one fifth of the diminution of the weight in ordinary circumstances.)

"Thus, the higher the column is, the greater is the ascending force, and the rushing in of the surrounding air on all sides will be produced with more energy. To understand this effect better, let us consider a mass of warm and dry air rising in the midst of a colder atmosphere. In proportion as this air rises, it will expand, because of the less pressure which it will experience, and consequently become colder; it will arrive then quickly at an equilibrium both of temperature and pressure with a layer more or less elevated, which it will soon reach, and in which it will remain; but if this only cause of cold, expansion, is overbalanced by a cause of heat, for example the heat furnished by the vapor which is condensing, this air will remain constantly warmer than would have been necessary to attain the same temperature and pressure as the surrounding air. It will then be constantly lighter, and the higher the column, the greater the ascending force.

"The calculations of Mr. Espy show, without the slightest doubt, that the column of damp air regaining in temperature, by the condensing of the vapor, a part of the heat lost by expansion; this column always remains warmer than the air which is at. the same height with each of its parts. Finally, Mr. Espy furnishes the exact data which are still wanting to science, by the experiments made upon the temperature which the air preserves by the effect of condensation of the vapor in a closed vessel which he calls a "nephelescope," and in which he compares the thermometrical fall produced in the air by a diminution of superincumbent pressure, to what takes place in nature, whether operating on dry, or employing damp, air. Notwithstanding the influence of the sides of the vessel, every time a light cloud is formed in the apparatus, the temperature undergoes a much less reduction than that which takes place when the point of precipitation of vapor has not been attained, or when the experiment is tried on dry air.

"The theory of Mr. Espy also accounts very well for the formation of a true cloud analogous to the cumulus with horizontal base, from the moment when the warm and damp air has acquired such an expansion, that the cold produced by it will cause a pre45

VOL. V.-NO. IV.