northwest, enlarging as they advance, and at latitude 30 inclining more to the north. Beyond this they curve to the northeast, and as far as he has been able to trace them, they pursue a direction more or less towards

the east.

Mr. Redfield has also attempted to show that in all our great storms, the wind gyrates in the form of a whirlwind; and in this he has been fol lowed on the other side of the Atlantic by Col. Reid, who has published a volume full of interesting details on the subject, in which he attempts to develop the law of storms by means of facts with a view to practical use in navigation. But neither of these gentlemen, so far as we know, have succeeded in tracing this supposed gyration to its cause, or pointed out the dependence between clouds, winds, hail, and the other phenomena of storms. Mr. Espy has taken a step beyond them, and confidently believes that he has discovered the key which is to unlock all the mysteries of meteorology, and disclose the hidden causes which produce clouds, water spouts, tornadoes, land spouts, variable winds, and barometric fluctuations. That result of Dr. Dalton's experiments on the aqueous vapor in the atmosphere, by which its amount in any given space may be determined by means of a glass of water and a thermometer, may be said to constitute the basis of Mr. Espy's theory, and therefore requires a passing notice. If the reader will take a tumbler of water of the same temperature as the air, and drop into it a small piece of ice, he will find, as the water cools, that dew will settle on the outside of the tumbler. The temperature at which this dew begins to form is called the dew point: and Dalton found, in the course of his experiments, that when it began to form at 32° fah., the amount of vapor suspended in the air was of the weight of the atmosphere that when the dew point was at 52° the air contained twice as much vapor as it did at 32° or of the weight of the atmosphere, and that when the dew point was at 73° the air contained four times as much vapor as at 32° or of the weight of the atmosphere.

The dew on the tumbler is condensed from the air by the cold communicated from the tumbler, and it may also be condensed by the same de. gree of cold produced in a different way. It is found that air is cooled by expansion produced by diminished pressure, and hence, when the receiver of an air pump is rapidly exhausted, and the air within expands sufficiently to cool it down to the dew point, moisture will make its appearance on the sides of the receiver, and an artificial cloud will appear. Mr. Espy supposes that it is precisely in the same way that clouds are formed in the laboratory of nature.

If a dozen feather beds were piled together one above another, the lower ones would be pressed closer than the upper, because they would not only have to sustain their own weight, but also the weight of all those above them. For the same reason the atmosphere which lies next to the surface of the earth, is subjected to much greater pressure than that which is piled up above, and this pressure must gradually decrease as you ascend. It follows then that if a current of air should pass upwards from the surface of the earth, it would be subjected to a constantly decreasing pressure, and would consequently expand: as it expanded it would grow cold, and when it reached the temperature of the dew point, it would begin to condense its vapor into sensible moisture, and thus form a cloud. This process, Mr. Espy contends, takes place constantly in the operations of nature. Certain portions of the air becoming more heated or more highly

charged with aqueous vapor than others, are thus made specifically lighter, and consequently rise, and when the dew point is high, these upmoving currents do not find their equilibrium until they are sufficiently expanded by the diminished pressure to which they are subjected to reduce their temperature to the point of forming dew, when a cloud will begin to appear.

The reduction of temperature which would thus be produced by the expansion of ascending air, Mr. Espy finds by experiment to be about one degree for every one hundred yards of ascent; and hence, if an upmoving current of air is ever produced in the operations of nature, it is easy to calculate how high it must rise before it begins to condense its vapor into visible cloud. For example: if, in a summer's day, the thermometer stands at 80°, and the dew point is 70°, then air must be cooled 10° before it will begin to condense its vapor into cloud. Consequently, if it cools one degree for every one hundred yards that it rises, then when it attains an elevation of ten hundred yards, it will be cooled down to the point of forming dew, when its vapor will begin to condense, and the base of a forming cloud become immediately visible. The bases of all forming clouds in the same neighborhood should therefore be nearly on the same level. Again: it is known to every chemist that vapor cannot be converted into water, without releasing a large quantity of caloric, known in technical language as the caloric of elasticity, and thus producing a considerable amount of sensible heat. If ice is exposed to heat, caloric combines with it and forms water; if water is exposed to heat, caloric combines with it and forms steam or vapor; and when vapor is converted back to water, this caloric (heat) must necessarily be released; and, according to Mr. Espy, its agency in producing wind, rain, hail, barometric fluctua tions, and all the sublime and astonishing phenomena which attend our most violent storms, has hitherto been altogether overlooked. He finds, by calculating according to well known chemical laws, that the caloric of

elasticity released during the condensation of vapor while a cloud is forming, will expand the air in the cloud about eight thousand cubic feet for every cubic foot of water formed by the process of condensation.

The expansion of the air in a cloud during the formation of water, is also proved by an instrument which Mr. Espy uses, called a Nephelescope, or cloud examiner. It consists of a glass vessel [b.] communicating with a bent tube [c.] con taining mercury, and having a forcing pump [a.] attached to it, by means of which any desirable quantity of air may be pressed into the receiver or glass vessel [b.] When the instrument is charged, the pressure on the inner leg of the mercury forces it up in the outer, and by carefully measuring the difference between the two, a given amount of pressure can be produced. When the air within (which is heated by the pressure) acquires the temperature of the air Vapor is five eighths the specific gravity of air.

without, the stop-cock is turned and the air permitted to escape until the mercury in both legs of the bent tube is on a level, when the stop is again closed. Now as the stop is closed at the moment the greatest cold is produced by expansion, the mercury in the outer leg will begin to ascend, and that in the inner leg to descend, and the difference of level at which they settle will indicate the reduction of temperature produced by a given expansion. But what the general reader is chiefly concerned to know in this experiment, is the fact that when moist air is used, and a cloud is formed in the receiver, the mercury in the outer leg of the bent tube is forced up higher than when dry air is used and no moisture is condensed, showing that the caloric of elasticity causes the air to occupy much more space when it is set free than when it is united to water in the form of vapor.* If this is true, and it seems to be placed beyond a doubt, then the air within a cloud is both lighter and warmer than that by which it is surrounded. That it is warmer is proved by actual observation as well as by Mr. Espy's experiments. Sausseur tells us that when he was enveloped in a cloud on the side of a mountain, his thermometer rose higher than in the sun; and both Durant and Gay-Lussac note the same fact while passing through clouds in a balloon. The uniform depression of the barometer under large clouds and during all our great storms, would seem also to confirm Mr. Espy's other position, and place beyond a doubt the fact that the air in the cloud is warmer, and therefore lighter than the surrounding atmosphere.

If, then, a cloud can be formed by a current of air moving upwards, and the cloud thus formed is lighter than the circumambient air, it necessarily follows that the equilibrium of the atmosphere must be more or less disturbed by every formation of this character. For if a lofty cloud by the evolution of its latent caloric, makes the air within it warmer and lighter, then will the air around it rush from all sides towards its base, and upwards into its centre; and as the wind in its upward course comes under less pressure, it will become gradually colder until it reaches the temperature of the dew point, when it will begin to condense its vapor, thus feeding the cloud with fresh materials for its expansion and perpetuity, and communicating to it, as it were, a self-sustaining power by which it moves on perhaps for days together, as we often behold in the operations of nature, enlarging as it advances, causing high winds wherever it passes, and fertilizing the earth with its refreshing showers.

"When a cloud begins to form from an ascending column of air, it will be seen to swell out at the top, assuming successively the appearances of 1, 2, 3, generally called cumuli: or, if the upmoving current should be driven out of its perpendicular motion by an upper current of air, the clouds which might then form would be ragged and irregular, called broken cumuli, as 4. These will always be higher than the base of cumuli, but much lower than cirrus. While the cloud continues to form and swell up above, its base will remain on the same level, for the air below the base has to rise to the same height before it becomes cold enough, by diminished pressure, to begin to condense its vapor into water; this will cause the base to be flat, even after the cloud has acquired great perpendicular height, and assumed the form of a sugar loaf. Other clouds, also,

When dry air is used in the experiment, the temperature, according to Mr. Espy, is reduced about twice as much as when moist air is used.

air at some distance above the surface of the earth, and below the base of the cloud, is sometimes very dry, and as much of this air goes in below the base of the cloud and up with the ascending column, large portions of the air in the cloud may thus not be saturated with vapor, and, of course, rain in this case will not be produced. These are some of the means contrived by nature to prevent upmoving columns from increasing until rain would follow. Without some such contrivances, it is probable that every upmoving column which should begin to form cloud when the dew point is favorable, would produce rain, for as soon as cloud forms, the upmoving power is rapidly increased by the evolution of the caloric of elasticity."

The cloud which produces water-spouts, land-spouts, and tornadoes, differs somewhat from other clouds, and can be formed only when the dew point is very high, the atmosphere devoid of cross currents, and the air in the neighborhood comparatively quiet, or rather, moving in the direction of the main current above. When these circumstances concur, and a cloud begins to form by an ascending column, there is nothing to prevent its rapid generation, and it shoots upward to a vast height, while it occupies only a small space in a lateral direction. The effects which follow the generation of such a cloud, must necessarily be more or less violent, because the whole force of the cloud is spent on a very small space. Extending upwards to a great height, and being lighter than the surrounding atmosphere, it takes off from the air below much of its accustomed pres sure, and the wind consequently presses in towards its base from all sides, and rushes up into the cloud itself with fearful velocity, carrying with it all light substances, uprooting trees, bursting off the roofs of houses, barns, and other buildings, and sometimes lifting into the air heavy timber, animals, and in one instance which we recollect, a cart loaded with potatoes. As the cloud is small in circumference, and is moved forward with considerable velocity by the main current in the higher region of the atmosphere, its progress brings it suddenly over the place which is to be the scene of its devastation; the accustomed pressure of the atmosphere is removed almost instantaneously; the barometer falls sometimes as low as two inches in the course of a few minutes, and the effect is analogous to that of an explosion. H. Tooley, who communicated to the secretary of the Albany Institute an account of the Natchez tornado, which took place on the 7th of May, 1840, has called particular attention to this last mentioned circumstance, and cited the following strong cases.

"1. The garret of a brick house occupied by Thomas Armat, Esq., as an office, was closely shut up, both ends bursted outward, and such was the force of the explosive power, that some of the bricks of the windward end were thrown upon a terrace nearly on a level with the end, and at a distance of not less than twenty feet in the face of the storm.

"2. A brick house on the north side of Main street, belonging to John Fletcher, had the leeward gable end thrown out, the windward end remaining uninjured.

"3. The windward gable end of a large house adjoining the Commercial Bank, bursted outward against the face of the storm; the leeward end was uninjured.

"4. The gable ends of a large three story brick house on Franklin street, owned by Rowan and Cartwright, were thrown outward with great force.