in regions where no volcano exists. Canada, in particular, is subject to such phenomena. In that country recourse has been had, for an explanation, to the burning of forests. The facts do not always appear to agree exactly with this supposition. Thus, on 16th October, 1785, at Quebec, clouds of such obscurity covered the sky, that it was impossible, even at noon, to see in what direction one was going. These clouds covered a space of 120 leagues in length by 80 broad. They seemed to come from Labrador, a country very thinly wooded; and they presented none of the characters of smoke.

On the 2d July, 1814, clouds similar to the above surrounded some vessels in the open sea on their way to the River St. Lawrence. The great obscurity lasted from the evening of the 2d till the

afternoon of the 3d.

With regard to the object we have here in view, it is of little importance whether we ascribe these clouds, capable as they are of completely obstructing the solar rays, to the burning of forests and savannas, or to emanations from the earth. Their formation, and their arrival in a given place, will remain equally beyond the predictions of science; the variations of temperature, and meteors of every kind which may be caused by these clouds, will never be pointed out beforehand in our meteorological almanacs.

The accidental darkening of the air, in 1783, embraced so extensive a space, (from Lapland to Africa,) that it was ascribed to the matter belonging to the tail of a comet, which, it was alleged, had mingled with our atmosphere. It is out of the question to maintain that an accidental state of the atmosphere, which enabled us, for a period of nearly two months, to look at the sun at mid-day with the naked eye, was without influence on terrestrial temperatures.

Forests cannot fail to exercise a sensible influence on the temperature of the surrounding regions; because, for example, snow remains there for a much longer time than in the open country. The destruction of forests, therefore, ought to produce a modification in our climates.

In given instances, what is the precise influence of forests, estimated by the centigrade thermometer? The question is very complicated, and has not hitherto been solved.

In all very mountainous regions, the valleys are traversed by periodical diurnal breezes, particularly sensible in May, June, July, August, and September. These breezes ascend the valleys, from seven or eight o'clock in the morning to three or four in the afternoon, the time when they reach their greatest force, and from four o'clock to six or seven in the evening. For the most part they blow with the force of a decided wind, and sometimes with that of a violent wind; they must, therefore, exert a sensible influence on the climates of the countries which lie around these valleys.

What is the cause of these breezes? Everything concurs to show that the cause is to be found in the manner in which the solar rays warm the central mass whence these valleys radiate. Suppose this mass to be naked, then you have a certain effect; substitute tufted forests for arid rocks, and the phenomenon will assume another character, at least with regard to intensity.

This is one of the twenty ways in which the clearing of woods affects climates. Before putting his hand to the task of arranging his predictions,

the manufacturer of almanacs ought, therefore, to enter into a correspondence with all the wood-cutters of every country.

In North America, the interior of the continent does not enjoy, in the same latitudes, the same climate as the coasts. By the influence of lakes, this difference disappears with respect to all the points where the distance from these great masses of water is not considerable.

We must, therefore, expect that the drying up of a lake will modify the climate of the neighboring region; and that a vast inundation, arising from the unexpected rupture of a barrier, will produce for a time an opposite effect.

If any one should exclaim against me on seeing me register causes, each of which, taken by itself, does not seem capable of producing a very great effect, my reply would be-We have to consider an influence as a whole, and in every case the perturbations which it is our object to explain, are far from being so extensive as the public supposes.

According to Howard, the mean temperature of London exceeds that of the neighboring country, about a centigrade degree (1o·8 F.)

The difference between the two temperatures is not the same at all seasons.

ELECTRICITY.

We could not well avoid arranging electricity among the causes which have a striking influence on climatological phenomena. Let us go farther, and inquire whether the operations of man may disturb the electrical state of an entire country.

Clearing the wood from a mountain is the destruction of a number of lightning-conductors equal to the number of trees felled; it is the modification of the electrical state of an entire country; the accumulation of one of those elements indispensable to the formation of hail, in a locality where, previously, this element was dissipated by the silent and incessant action of the trees. On this point, observations support theoretical deductions.

According to a detailed statistical account, the losses occasioned by hail in the continental states of the king of Sardinia, from 1820 to 1828 inclusively, amount to the sum of forty-six millions of francs. Three provinces, those of Val d'Aoste, the Vallée de Suze, and Haute Maurienne, do not appear in these tables; they were not visited with hail storms. The mountains of these three provinces are the best wooded.

Of the warmest provinces, that of Genoa, the mountains of which are well covered, is scarcely ever visited by this meteor.

Atmospheric electricity gives rise to phenomena, which are immense from their extent. They seem, however, to owe their origin to causes purely local. Their propagation likewise takes place under circumscribed influences, in particular zones, and these sometimes rather narrow.

On the 13th July, 1788, in the morning, a hailstorm commenced in the south of France, traversed, in a few hours, the whole length of the kingdom, and thence extended to the low countries and Holland.

All the districts in France injured by the hail, were situated in two parallel bands, running south-west and north-east. One of these bands was 175 leagues long; the other about 200.

The mean breadth of the most western hail band was 4 leagues, the other only 2 leagues. On

The damage occasioned in France, in the 1039 parishes visited by the hail, appeared, from official inquiry, to amount to twenty-five millions (one million sterling.)

This, certainly, must be regarded as a considerable atmospheric commotion, whether we regard the material devastation it produced, or the influence which the displacement of the air, and the mass of hail deposited on the surface of two long and broad bands of country, must have exercised on the normal temperature of a great number of places. Could meteorologists, however skilled, have been able to foresee it?

The origin of the two bands was in the district of Aunis, and in Saintonge. Why there, and not elsewhere? Why did not the storm commence at another point of the parallel of latitude, passing by its meridional extremities? Because, it will be answered, in Aunis and in Saintonge, on the 13th July, 1788, the conditions of electricity and temperature were eminently favorable for the production of a hail-storm, and an accompanying hurricane directed from the south-south-west to the north-north-east. Admitted; but were not these thermal and electrical conditions favorable to the production of a storm, ultimately connected with agricultural operations, with the existence of such and such a mass of trees, with the state of irrigation, with circumstances varying according to the wants and caprice of men? With regard to temperature, no one can hesitate in his reply. In the other particular, the connection will appear not less evident if I bring to mind that evaporation is a fertile source of electricity, and that various natural philosophers have even included vegetation among the causes which generate this same fluid in the atmosphere.

If it be true, as has been alleged, that, in certain cases, the flame and smoke which issue from the mouth of a furnace, or from the chimney of a manufactory, may deprive the atmosphere of all electricity for many leagues around, the prophets in meteorology, will be placed in an additional difficulty. It will be necessary that they should know beforehand all the plans of the masters of forges and proprietors of manufactories.

According to all that we most certainly know respecting the physical cause of water-spouts, and according to M. Espy's theory, sometimes no more is necessary than an ascending current produced by the chimney of a manufactory, to give rise to one of these formidable meteors.

RAIN.

It is said to have been remarked in Italy, that, in proportion as rice-fields multiply, the annual quantity of rain has gradually increased, and that the number of rainy days has augmented in proportion.

Can it be imagined, that such circumstances as these can ever be taken into account, in the combinations of the almanac-manufacturers?

The following passage occurs in Bacon's works: "Some historians allege that, at the time when Guyenne was still in the power of the English, the inhabitants of Bordeaux and the neighboring cantons made a request to the king of England, to induce him to prevent his subjects of the counties of Sussex and Hampton, from burning the heaths in the end of April, as they usually did; because they thereby gave rise, it was affirmed, to a wind which proved very hurtful to their vines."

I know not how far there were grounds for this request, as the distance of Bordeaux from the county of Sussex is very considerable; but I must not fail to mention, that natural philosophers are now disposed to assign a no less extraordinary part to conflagrations. In the United States, a well known philosopher, M. Espy, adopting the opinions prevalent among the natives of the new continent, from Canada to Paraguay, has recently proposed to produce, in times of drought, artificia rains, and his means of doing so is by kindling large fires. In support of his scheme, M. Espy mentions the following :

The opinion of the Indians of Paraguay, who, according to the report of the missionaries, set fire to vast savannas when their crops are threatened with drought, and allege that they thus produce even storms accompanied with thunder;

The opinion of the colonists of Louisiana, and the success from time immemorial of burning the prairies in that State;

The opinion of the population of Nova Scotia, respecting the consequences of burning forests; The opinion and practice of the colonists of the districts of Delaware and Otsego, &c., &c.

M. Espy says, that he has assured himself, in various ways, that the climate of Manchester has undergone gradual and sensible modifications, in proportion as manufacturing industry has increased. Since that city has become, so to speak, a vast furnace, it rains there more or less every day. Those who pretend that the deterioration of the climate is not so considerable, assure us that it does not rain at Manchester more than six days in the seven!

Suppose these facts to be as averred. The predictions of rain, in a given place, will often he overturned by accidental fires, and by the fires of manufactories.

Space and time will not allow me to point out the multitude of local causes which may exercise a great influence on the direction and force of the wind. I shall discuss this delicate question in another notice. At present, I shall confine myself to a remark well-fitted to enlighten those who, from want of meteorological instruments, take for their guides the state of the crops and of vegetation. It may be expressed in the following formu

antry in the south of Scotland (we know not whether the belief prevails elsewhere,) that muir-burn, or the burning, in the spring, of old heather and other plants, in order to produce a more tender and nutritious vegetation, a practice which was once very general, has a decided tendency to produce a change of weather, and to bring on

The direct influence of the wind, on the phenomena of vegetation, is nowhere more strikingly exemplified than in the Isle of France. The south-east wind, very healthy both for men and animals, is, on the contrary, a perfect scourge to the trees. Fruit is never found on the branches directly exposed to this wind; none is to be found but on the opposite side. Other trees are modified even in their foliage; they have only half a head, the other has disappeared under the action of the wind. Orange and citron trees become superb in the woods. In the plain, and where they are without shelter, they always continue weak and crooked.*

From the Edinburgh Philosophical Journal.

On the Surface of the Moon. By Captain ROZET. M. ELIE DE BEAUMONT has already been enabled, by means of the beautiful selenographic delineations of Lohrmann, and of Beer and Mädler, to make some very remarkable comparisons between the forms presented by certain portions of the mountainous masses of the earth, and the annular openings of the surface of our satellite.

During the summer of 1844, one of my friends having directed my attention to the circular forms of nearly the whole of the variations of the lunar surface, I have devoted myself since that time to the study of the phenomena presented by these variations of surface, having, at the same time, called in the aid of the beautiful German maps, and of various works already published on the subject.

The contours of all the great greyish spaces which, for a very long time, have been termed Seas, although it is known with certainty that they cannot be masses of water, are formed by arcs of circles which intersect one another. The number of arcs sometimes amounts to two, rarely to one mare crisium. These contours present circular escarpments which seem perpendicular, but the inclination of many of which is 45 degrees. The matter composing them appears to be swelled up, and their height often exceeds 4000 metres (upwards of 13,000 English feet.) In the interior of the seas we remark annular openings or perfect rings, whose diameter amounts to 10 myriametres (upwards of 60 English miles,) and the height of whose terminal ridge is 4000 metres. Several of them have a peak in the centre, which is a little less elevated than the edges of the ring.

The large grey spots cover a great portion of the northern, eastern, and western regions of the disc, and leave in its southern part a brilliant space, covered with an infinity of rings of all dimensions. These rings are simple and isolated, complex, or united together, two and two, three and three, &c. When they touch one another. the contours are always rendered imperfect; and it is generally the smaller one which encroaches on the larger. In the interior of the large rings there are almost always present sinaller ones, which cut the edges when they touch them. The bottom of the rings seems to be flat, but that bot

*Annuaire pour l'an 1846.

arcs of circles parallel to the external ridge; so that the rings would seem to have been formed at the surface of a fluid mass on which scoria were floating, by means of a circular undulation, whose amplitude went on diminishing.

The bottom of the great spots, such as the mare serenitatis, &c., exhibits the same characters. Simple spots are also to be noticed, or portions having no projection, but whose circular forms are well marked. It cannot, therefore, be called in question, that a general cause, producing these circular forms, has had an immense influence in the formation of the solid crust of our satellite. We can perfectly account for all the facts now enumerated, by supposing a number of whirlpools in the fluid matter, whose amplitude diminished with the fluidity of that matter. Nothing is to be seen on the surface of the moon which reminds us of our chains of mountains with their lateral branches, or of our great valleys with their numerous ramifications, &c. We see, indeed, many well marked fissures, as, for example, at the bottom of the mare diverge from one centre, as in Tycho, Copernicus, vaporum; but these fissures are simple; several Kepler, &c., and form radiating cracks, analogons to those in Von Buch's craters of soulevement, but much more considerable. One of the fissures of Tycho traverses the moon diametrically. A continued study of the various portions of the moon, under all inclinations of the solar rays, enables us to recognize two layers which are quite distinct, but two layers only;-the bottom of the great greyish spaces, which is also that of the rings; and a scoriaceous crust, elevated above that bottom to a height which has been measured at a great number of points. These measurements have afforded me the means of calculating the thickness of this crust, and I found that the mean is 642 metres (2106 English feet.)

From all the facts I have ascertained, and from all the deductions to which these facts have led me, I think I may draw the following conclusions:

1. The lunar globe has originally been in a state of fusion, and has been gradually cooled. 2. During the formation of the external scoriaceous pellicle, there existed in the mass whirlpools or circular movements, which, driving the scoria from the centre to the circumference, formed annular ridges, by the accumulation of those scoriæ at the limit of the undulation. When several whirlpools occurred in such circumstances, that the distance of the centres, taken two and two, was less than the sum of the radii, there resulted an enclosed space, bounded by arcs of circles. When the distance of two centres was greater than the sum of the radii, two complete rings were formed.

3. The amplitude of the whirlpools diminished with the fluidity of the surface, but the phenomenon continued throughout the whole duration of the process of consolidation.

4. The mode of formation which we assign to the lunar rings, altogether excludes the idea of craters resembling those of our volcanoes.

5. The surface of our satellite being thus consolidated, no solid or liquid layer coming from the exterior was subsequently deposited upon it; for, otherwise, the small rings and the fissures would have disappeared. The perfect preservation of all these variations in external configuration, shows that no liquid has ever existed in considerable quantity, either at the surface, or even in the atmosphere of the moon.