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tion, we shall now enter more immediately on the subject of the electrical phenomena of the atmosphere, together with the explanations of many others which arise necessarily out of the adoption of the theory I have to propound.

It is admitted on all hands that the air is always charged, to a greater or less degree, with transparent aqueous gas, or vapour.

It is also admitted, that a column of atmosphere moving upwards, will lose, by diminished pressure, 1° of Fahrenheit for every one hundred yards it ascends from the earth.

Whenever transparent vapour is formed at the surface, the law of diffusion will cause it to ascend, perhaps aided—but on this I do not insist-by its specific gravity, it being only five-eighths of that of the atmosphere. The circumstances of the locality will, in some degree, accelerate or retard.

Whenever this vapour ascends high enough in the atmosphere, it will be cooled down, according to a fixed law, until it forms cloud.

The height at which this phenomenon takes place can be readily ascertained, at any given period, by the application of Dr. Dalton's great discovery of the dew-point; the height varying with the mean temperature and the amount of aqueous vapour contained in the air.

Whenever this change takes place, namely, the formation of cloud out of transparent aqueous gas, this body becomes decomposed, that is, its water, as such, is set at liberty, with about 1072° Fahrenheit of latent caloric, which was before insensible.

The caloric thus liberated expands the surrounding air enormously, and, from its levity, rushes upwards. This rush causes a corresponding movement in the outer circles of the atmosphere, and gives rise to one great section of meteorological phenomena, consisting of winds, storms, and tornados, well explained by Mr. Espy.

The water, which was before combined chemically in the gaseous state, is resolved into small globules of water, and forms what we term cloud. It is this cloud that furnishes materials for rain, hail, and snow.

When, however, this chemical change or decomposition of transparent aqueous vapour takes place, it is attended with another all-important, but hitherto unnoticed, phenomena, namely, the developement of a definite and necessary portion of electricity, whose force can be measured with as much accuracy as that of the latent caloric developed during the same phenomenon. It is the electricity developed during this change that causes thunder-storms, lightning of every description, violent storms of hail, water-spouts, and aurora borealis.

When the latent caloric is abstracted from the water, were it not for the electricity developed simultaneously, this water would be precipitated at once to the earth, in sheets or streams, or irregular spouts, or in fog or mists, according to the quality liberated; and

we never should have any permanent cloud floating in the atmosphere under any possible circumstances.

The electricity thus developed attaches itself to the small globules of water when liberated, and surrounds their surface, giving them more or less tension, according to the amount of aqueous vapour present in a given space when the change takes place.

The surface of all the globules of water composing a given cloud having a like amount of positive electricity, are repelled from each other by the well-known law of electrical repulsion between similarly electrified bodies: the consequence is, that the cloud remains permanent, and is floated off by the next current, as an immense Leyden jar possessing an enormous amount of free electricity.

A cloud, formed under the circumstances I have stated, and floated off amongst others into the atmosphere, may be said to possess its natural portion of electricity ; that is, that portion which forms one of the necessary conditions of its being a cloud at all. Clouds formed under those circumstances comprehend the aggregate of all the clouds formed ; and it would not be too much to say, that, in our variable climate, for one storm-cloud there are 10,000 formed that are not so.

In tropical climates, or in our own in summer, when the air is surcharged with aqueous gas by the immense evaporation that has taken place, and when there are no disturbing currents of any magnitude, a small cold current in the upper regions of the atmosphere will commence the process of cloud forming, which, under those circumstances, takes place with fearful rapidity, and, from the size of a dark speck, expands itself into an immense black canopy, darkening the face of the atmosphere, and it is only by some disturbing current that it comes in contact with on the other hand that the process stops.

Clouds formed under these latter circumstances, it is obvious, will

possess a much greater portion of electricity than those I have previously adverted to, because they are formed in an atmosphere containing an extraordinary quantity of aqueous gas, and the air, from a comparatively large circle, rushes to the spot; when discharged of its gas, the whole of the electricity liberated is contained in such clouds. These clouds, then, are the true storm or thunder clouds, because they possess more than what I have already termed their natural portion of electricity.

Let us now take a cloud formed under the circumstances just detailed, and one or a series of those formed under ordinary circumstances. In the first place, it will be evident to all electricians, and, indeed, to those having the slightest knowledge of this force, that clouds formed under the different circumstances named will be positive and negative to each other; that is, the cloud formed under ordinary circumstances will be negative as respects the cloud just termed the storm-cloud, -the one will possess more electricity than

the other. Let us now suppose, that the storm, or positive, cloud is floating in the atmosphere, and let it be borne in mind, that such clouds are generally higher or at greater distance from the surface of the land or water than the clouds formed under ordinary circumstances. This is said to arise from the air contained within the cloud being at a higher temperature than the surrounding atmosphere, and, in consequence of this rarefaction, their altitude is generally superior.

The storm-cloud is then carried by a current to the neighbourhood of a cloud that is negative with respect to itself. Whenever it comes within the sphere of its attraction, a discharge of the superabundant electricity takes place.

This discharge may take place under any of the following circumstances :

First, the storm or thunder cloud may be a very large one, and, consequently, possess an immense quantity of free electrical force. If it comes in contact with a small negative cloud, a sharp clap of thunder, accompanied by a short shower of large dropped rain, will be the result, and the lightning given out will be by no means vivid. In summer, in our climate, such discharges often take place.

The small negative cloud that has just received the discharge from the large positive one now becomes in the same electrical state, and they roll off together. Both of the clouds now become positive with respect to ordinary clouds, but the larger positive one has diminished in bulk just in the ratio of the rain that has fallen, and a portion of the electricity of the cloud is carried to the earth or sea on the surface of the drops of rain. Thus agriculturists well know that a shower of rain will do more to hasten vegetation than nearly double the amount of water added to the soil by artificial means. This arises from the positive electricity, which, it is now well known, gives an immense impulse to vegetation.

Should the two clouds that have now become positive come in contact with a series of negative clouds, sharp, rattling peals of thunder take place like the, discharge of artillery, seriatim, and forked lightning is the result, accompanied by tremendous showers of heavy, large dropped rain. In tropical climates, under such circumstances, from the quantity of water held in solution in the atmosphere, the water descends literally in sheets. This rain, or rather what is usually termed the thunder shower, will take the direction of the discharge of electricity ; that is, supposing the storm-cloud to be situated due north, and the end of a series of negative clouds to be south as respects the positive one, then rain will begin north and end south. During the continuance of a storm of this description, should the electricity or lightning pass off into the earth, or be conducted into it by any prominent object thereon, then the air will suddenly brighten : the dense black cloud will disappear, because it has been really annihilated, as a cloud, hy the

electrical discharge that has taken place on the earth ; but, on the other hand, should the electricity not pass off to the earth, but be diffused through a mass of negative cloud, as soon as the transference takes place, this before comparatively-white cloud will assume the gloomy appearance of the primary thunder cloud, but never quite so dark to the eye, as a portion of the electricity was passed off to the earth with the rain. A thunder storm of the kind I have just detailed may be attended with another phenomenon which has been often set down as the echo or reverberation of the primary peals of thunder. This is caused by one of the most beautiful, yet no less wonderful, laws attending the movement or transference of this universal force. The idea of an echo or reverberation of sound is, when we take into view the materials (clouds) that are to reflect it, one that, on a little consideration, will appear to be quite untenable, and only tends to show the utter absence of the application of well known laws to explain these apparently enigmatical, but equally simple, occurrences.

To explain this, let us suppose that which often takes place according to the circumstances of the atmospherical currents, that another series of clouds are in the same stratum of atmosphere, and, at the same time, exactly opposite the series where the thunderstorm is taking place, and the direction of the discharge from north to south, as already predicated. The consequence of this state of things would be, that another series of actual discharges, accompanied with thunder, would take place in the other opposing series of clouds, but from south to north, and at the same time, much weaker in all the accompanying phenomena. This is caused by the law of electrical induction, which shows us, that no disturbance of electrical equilibrium can, by possibility, take place in one body, or a series of them, without causing a similar disturbance in any other conducting body in the vicinity. A series of clouds may be above or below the primary series, or they may be in almost any given position as relates to the primary, yet they will be necessarily disturbed by the first great discharges, and weaker peals of thunder will be the result, and at very opposite points of the compass.

All these various discharges will be attended with large dropped rain, and, if there is any echo or reverberation attending a thunderstorm, it must be in alpine districts, where the sound is re-echoed from hill to valley, and, even here, such must necessarily be of rare occurrence, as the peaks themselves serve as so many conductors that extract the electrical intensity from the clouds, while the water is descending in drizzling rain.

It is this attraction of the clouds to mountains that gives rise to many of the phenomena that influence the seasons in large districts, as on the Chilian and Peruvian side of the Andes we find a rainy season for many months of the year on the one side, while, at the

same time on the other side of the same ridge the land and vegetation is parched and dried for want of water.

With my present views, the explanation of this or similar phenomena becomes at once simple and easy.


be said the Andes occupy the sea coast of one side of South America, with the vast Southern Pacific stretching out at their feet ; while, on the other side, the immense plains of the Pampas extend for many hundred miles before they reach the Atlantic. In consequence of this relative position, as respects the ocean on the one hand and the land on the other, the mountain-peaks on the side next the Pacific attract the clouds that are formed by the water evaporated from its surface ; but, from the height of the mountains themselves, they being much higher than that portion of the atmosphere usually occupied by clouds, rain can never get an opportunity to fall on the other side, because the clouds are really stopped in their progress and annihilated before they can by possibility reach it. This attraction of clouds by mountains has been long known and observed; but the true explanation is, not that the mountain attracts the cloud per se, but that the mountain, as a conductor of electricity, attracts the free electric fluid contained in the cloud to its vicinity. The cloud is, consequently, discharged of its electricity; then follows a precipitation of the water in the form of rain.

There are, occasionally, rare exceptions to this rule, where it is observed that the clouds are not always attracted by mountain peaks, and, when driven to their vicinity by a current, do not always discharge their rain. In such cases, the mountain is in the same electrical condition as the clouds, and, consequently, no action will take place in either body,


CONVERSAZIONE, JANUARY 6TH, 1842. In Continuation of a Communication read on the 9th December, 1841.


On the last occasion of my addressing this Institution, I explained the causes of the prevailing injuries to boilers, and proved that we were mistaken as to some of them. I shewed that the sediment in boilers assumes two different forms--namely, that of a chrystallised solid incrustation, and that of a loose mud-like body, held merely in suspension.

I proved that the first could not be the cause of injury, inasmuch as it was, of itself, a good conductor of heat; whereas the secondthe floating matter--became a positive non-conductor, after the

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