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LITTELL'S LIVING AGE.-No. 119.-22 AUGUST, 1846.

From the Edinburgh New Philosophical Journal.
ARAGO ON THE WEATHER.

I repeat, that the readers of the Annuaire ought not to expect to find here a complete investigation of the problem which I have taken up. My sole Is it possible, in the present state of our knowledge, intention is to lay before them a few facts, which, to foretell what Weather it will be at a given time taken in connexion with those which I shall anaand place? Have we reason, at all events, to ex-lyze in a second notice, appear to me to lead to pect that this problem will one day be solved? By this conclusion. M. ARAGO, Perpetual Secretary of the French Academy of Sciences, &c. &c.

BETWEEN WHAT LIMITS THE MEAN TEMPERATURES
OF YEARS AND MONTHS VARY IN OUR CLIMATES.

ENGAGED as I am, both from inclination and duty, in meteorological studies, I have often asked The meteorological state of a given place, is myself if we should ever be able, by a reference to much less variable than those would be led to beastronomical considerations, to determine, a year lieve who judge of it by their personal sensations, in advance, what shall be the state, in a given by vague recollections, or the condition of the place, of the annual temperature, the temperature crops. Thus, at Paris, the mean temperature of of each month, the quantities of rain compared years ranges within very narrow limits. with the ordinary mean, the prevailing winds, &c. I have already laid before the readers of the Annuaire the results of the investigations undertaken by natural philosophers and astronomers, regarding the influence of the moon and of comets on the changes of the weather. These results clearly show, in my opinion, that the influences of both these bodies are almost insensible, and, therefore, that the prediction of the weather can never be a branch of astronomy, properly so called. And yet our satellite and comets have, at all periods, been considered as preponderating stars in meteorology.

year

The annual mean temperature of Paris, from 1806 to 1826 inclusive, has been +10°-8 centigrade, (54°-4 Fahr.) The greatest of 21 annual means does not exceed the general mean by more than 10.3, (20-3 F.;) the lowest of the mean annual temperatures has been found below the general mean only by 10.4, (20.5 F.) As far as relates to mean annual temperatures, systematic meteorologists have, therefore, no need of foresight to predict only slight perturbations. The causes of disturbance will satisfy all the phenomena, if they can produce, more or less, 10.5 of centigrade variation, (20.7 F.)

It is not the same with regard to the months. The differences between the general means and the partial means extend, in January and December, to 4 and 5 centigrade degrees, (7° to 9° F.)

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Since the publication of these opinions, I have regarded the problem in another aspect. I have considered whether the operations of man, and occurrences which will always remain beyond the range of our foresight, might not be of such a nature as to modify climates accidentally, and in a from indulging in any illusion on this subject. Hundreds very sensible manner, in particular with regard to of persons who have gone through a regular course of temperature. I already perceive that facts will university studies, will not fail, in 1846, as they had done on former occasions, to ply me with such questions as the answer in the affirmative. I should have wished, following, which it is truly pitiable to hear in the present however, not to publish this result till after I had day: Will the winter be severe? Think you that we finished my investigations; but I must frankly own, shall have a warm summer, a humid autumn? This is that I wished to have an opportunity of protesting very long and destructive drought; do you think it is decidedly against the predictions which have every produce great mischief this season-what is your opinnear an end? People think that the April moon will been attributed to me, both in France and in on? &c. &c. In spite of the little confidence I have in other countries. Never has a word escaped my predictions, I affirm that in this case the event will not lips, either in private or in the course which I have deceive me. Nay, for some years past have I not been delivered for upwards of thirty years; never has a put to a still severer proof? Has not a work been published, entitled "Lectures on Astronomy, delivered at the line published with my consent, authorized any one Observatory by M. Arago, collected by one of his Pupils ?" to imagine it to be my opinion that it is possible, I have protested a dozen times against this work; I have in the present state of our knowledge, to announce, shown that it swarms with inconceivable errors; that it with any degree of certainty, what weather it will is beneath all criticism whenever the author ceases to embe a year, a month, a week, I shall even add, a ploy his scissors on the notices of the Annuaire, and is reduced to the necessity of drawing a few lines from his single day, in advance. May the indignation I own resources. Vain efforts! These pretended Lectures have felt at seeing a multitude of ridiculous predic- on Astronomy at the Observatory have, however, reached tions appear under my name, not constrain me, by no less than a fourth edition. The laws have made no the force of reaction, to give an exaggerated de- provision against what I shall call this scientific calumny. gree of importance to the disturbing causes I have What must be done when the law is silent? Submit with resignation? A sensitiveness which will not appear surenumerated! At present, I believe that I am in a prising to any who have seen the book in question, will condition to deduce from my investigations the im- not allow me to be satisfied with resignation. My posiportant result which I now announce; Whatever tion having become intolerable, I have made up my mind may be the progress of sciences, NEVER will observers to publish myself the Lectures which have been so outwho are trust-worthy, and careful of their reputa-shall abandon for a time the plans for original investigarageously disfigured. Since it has become necessary, I tion, venture to foretell the state of the weather.*

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tions which I had formed, and devote the time I wished to employ in delicate experiments, fitted to illustrate points of the science still enveloped in great obscurity, to the preparation of a work intended to popularize astronomy. May this work be in some degree useful.

In consequence of these variations, if we compare the extreme temperatures of each month with the mean or normal temperatures of all the rest, we shall find::

That the month of January is sometimes as temperate as the mean of the month of March.

That the month of February sometimes resembles the mean second fortnight of April, or the mean first fortnight of January.

That the month of March sometimes resembles the mean of the month of April, or the mean of the second fortnight of January.

That the month of April never reaches the temperature of the month of May.

That the month of May is pretty frequently, in the mean, warmer than certain months of June. That the month of June is sometimes, in the mean, warmer than certain months of July.

That the month of July is sometimes, in the mean, warmer than certain months of August.

That the month of August is sometimes, in the mean, slightly colder than certain months of September.

That the month of September is sometimes, in the mean, colder than certain months of October.

That the month of October may be, in the mean, nearly 3° (50.4 F.) colder than certain months of November.

That the month of November may be, in the mean, about 50.5 (about 10° F.) colder than the warmest months of December.

That the month of December may be, in the mean, 7° (12°.6 F.) colder than the month of Jan

uary.

climates, is that known by the English name of icebergs. These mountains of ice come from the glaciers, properly so called, of Spitzbergen or the shores of Baffin's Bay. They detach themselves from the general mass, with a noise like that of thunder, when the waves have undermined their base, and when the rapid congelation of rain-water in their fissures produces a sufficient expansion to move these huge masses and push them forward. Such causes, and such effects, will always remain beyond the range of human foresight.

Those who remember the recommendations which the guides never fail to give upon approaching certain walls of ice, and the huge masses of snow placed upon the inclined ridges of the Alps; those who have not forgotten that, according to the affirmations of these experienced men, the report of a pistol, or even a mere shout, may produce frightful catastrophes, will agree in the opinion I have just expressed.

Icebergs often descend without melting, even to pretty low latitudes. They sometimes cover immense spaces; we may therefore suppose that they sensibly disturb the temperature of certain zones of the oceanic temperature, and then, by means of communication, the temperature of islands and continents. A few instances of this will not be out of place.

On the 4th October, 1817, in the Atlantic Ocean, 46° 30 north latitude, Captain Beaufort fell in with icebergs advancing southwards.

On the 19th January, 1818, on the west of Greenspond, in Newfoundland, Captain Daymont met with floating islands. On the following day, the vessel was so beset with ice that no outlet

DISTURBING CAUSES OF TERRESTRIAL TEMPERATURE could be seen even from the top-masts. The ice,

WHICH CANNOT BE FORESEEN.

The atmosphere which, on a given day, rests upon the sea, becomes in a short time, in mean latitudes, the atmosphere of continents, chiefly from the prevalence of westerly winds. The atmosphere derives its temperature, in a great measure, from that of the solid or liquid bodies which it envelops. Everything, therefore, which modifies the normal temperature of the sea, produces, sooner or later, perturbations in the temperature of continental atmospheres. Are those causes, which may sensibly modify the temperature of a considerable portion of the ocean, placed forever beyond the foresight of man? This problem is closely connected with the meteorological question I have undertaken to consider. Let us endeavor to find the solution of it.

No one can doubt that the ice-fields of the Arctic pole-the immense frozen seas-exert a marked influence on the climates of Europe. In order to appreciate in numbers the importance of this influence, it would be necessary to take into account at once the extent and position of these fields; but these two elements are so variable that they cannot be brought under any certain rule.

The eastern coast of Greenland was in former times accessible and well peopled. All of a sudden an impenetrable barrier of ice interposed itself between it and Europe. For many ages Greenland could not be visited. About the year 1815 this ice underwent an extraordinary breaking up, became scattered in a southerly direction, and left the coast free for many degrees of latitude. Who could ever predict that such a dislocation of the fields of ice would take place in such a year rather

than in another?

The floating ice which ought to act most on our

for the most part, rose about 14 English feet above the water. The vessel was carried southwards in this manner for twenty-nine days. It disengaged itself in 44° 37′ latitude, 120 leagues east of Cape Race. During this singular imprisonment, Captain Daymont noticed upwards of a hundred icebergs.

On the 28th March, 1818, in 41° 50′ north latitude, 53° 13′ longitude west of Paris, Captain Vivian felt, during the whole day, an excessively cold wind blowing from the north, which led him to suppose that ice was approaching. And, in fact, on the following day, he saw a multitude of floating islands, which occupied a space of upwards of seven leagues. "Many of these islands," says he, "were from 200 to 250 English feet high above the water."

The brig Funchal, from Greenock, met with fields of ice on two different occasions, in her passage from St. John's, Newfoundland, to Scotland; first on the 17th January, 1818, at the distance of six leagues from the port she had left; and afterwards, in the same month, in latitude 47° 30'. The first field was upwards of three leagues broad, and its limit in a northern direction could not be seen. The second, likewise very extensive, had an immense iceberg in its centre.

On the 30th March, 1818, a sloop of war, The Fly, passed between two large islands of floating ice in 42 degrees of north latitude.

On 2d April, 1818, Lieutenant Parry met with icebergs in 42° 20′ of north latitude.

This year (1845) the English vessel Rochefort continued enclosed, at the end of April and beginning of May, for twenty-one consecutive days, in a mass of floating ice, which ran along the bank of Newfoundland, advancing to the south.

The sea is much less easily heated than the land, and that, in a great measure, because the water is diaphanous. Everything, therefore, which causes this diaphaneity to vary considerably, will produce sensible changes in the temperature of the sea, immediately after in the temperature of the oceanic atmosphere, and, somewhat later, in the temperature of the continental atmosphere. Do causes exist, independently of what science discovers to us, which may interfere with the transparency of the sea to a great extent? Let the following be my answer :

Mr. Scoresby has shown, that, in northern regions, the sea sometimes assumes a very decided olive-green color; that this tint is owing to medusæ and other minute animalculæ ; and that wherever the green color prevails the water possesses very little diaphaneity.

Mr. Scoresby occasionally met with green bands, which were from two to three degrees of latitude (60 to 80 leagues) in length, and from 10 to 15 leagues broad. The currents convey these bands from one region to another. We must suppose that these do not always exist; for Captain Phipps, in the account of his voyage to Spitzbergen, makes no mention of them.

As I have just stated, the green and opaque portions of the sea must become heated in a manner different from the diaphanous parts. This is a cause of variation in the temperature which can never be subjected to calculation. We can never know beforehand whether, in such and such a year, these countless myriads of animalcula will be more or less prolific, and what will be the direction of their migration southwards.

The phosphorescence of the sea is owing to minute animals of the medusa kind. The phosphorescent regions occupy very large spaces-sometimes in one latitude, sometimes in another. Now, as the water of the phosphorescent spaces is quite turbid, and as its diaphaneity is almost entirely destroyed, it may become, by its abnormal heating, a cause of notable disturbance in the temperature of the oceanic and continental atmospheres. Who can foresee the intensity of this cause of thermic variation? who can ever know beforehand the place which it occupies?

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These differences belong to the localities. But when concealed local circumstances exert so much influence, is it not natural to think that the modifications which they receive from the hand of man may sensibly alter, in the interval of a few years, the meteorological type of every town in Europe?

I have shown that local circumstances which are latent, or at least faintly characterized, may exert sensible and constant influences on the manner in which the maxima and minima of temperature are distributed in the year. When science shall be put in possession of exact and comparable meteorological observations, made simultaneously in different places; when these observations shall be scrupulously and judiciously digested, we shall very probably find that circumstances of locality will occupy a much more prominent place in science than natural philosophers seem now disposed to attribute to them. It would not be difficult for me, at this moment, to mention circumscribed districts which have completely escaped the severe colds to which the surrounding countries were subjected. The Sables d'Olonne, for example, and the neighboring districts, six leagues in circuit, formed, during the winter of 1763 and 1764, a kind of thermal oasis. The Loire was frozen near its mouth; an intense cold of -10 degrees centigrade (14° F.) interrupted all agricultural operations in the districts which the river traverses. Sables the weather was mild: this little canton escaped the frost.

In the

The following is a still more extraordinary fact than the preceding, for it takes place every year.

There is in Siberia, M. Erman has informed us, an entire district, in which, during the winter, the sky is constantly clear, and where a single particle of snow never falls.

Let us suppose the atmosphere immobile and perfectly clear. Let us suppose, moreover, that the soil has everywhere, in an equal degree, ab- I am willing to overlook the perturbations of the sorbing and emissive properties, and the same terrestrial temperatures which may be connected capacity for heat; we should then observe through- with a greater or less abundant emission of light or out the year, as the effect of solar action, a regular solar heat, whether these variations of emission and uninterrupted series of increasing temperatures, depend on the number of spots which are found and a corresponding series of decreasing tempera-accidentally scattered over the sun's surface, or tures. Each day would have its invariable temperature. Under every determined parallel, the days of the maximum and minimum of heat would be respectively the same.

whether they originate in some other unknown cause; but it is impossible for me not to draw the reader's attention to the obscurations to which our atmosphere is from time to time subject, without any assignable rule. These obscurations, by preventing the light and solar heat from reaching the earth, must disturb considerably the course of the seasons.

This regular and hypothetical order is disturbed by the mobility of the atmosphere; by clouds more or less extensive, and more or less permanent; and by the diverse properties of the ground. Hence the elevations or depressions of the normal heat of Our atmosphere is often occupied, over spaces days, months, and years. As disturbing causes of considerable extent, by substances which matedo not act in the same way in every place, we may rially interfere with its transparency. These matexpect to see the primitive figures differently mod-ters sometimes proceed from volcanoes in a state ified; to find comparative inequalities of tempera- of eruption. Witness the immense column of ture where, from the nature of things, the most perfect equality might have been looked for.

Nothing is better calculated to show the extent of these combined disturbing causes, than the comparison of mean epochs, indicating the maxima and

ashes which, in the year 1812, after having been projected from the crater of the island St. Vincent to a great height, caused at mid-day a darkness like that of night in the island of Barbadoes.

These clouds of dust appear, fr ́m time to time

That the month of Imuary is sometimes as temperte as the me in of the month of March.

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In consequence of these variations, if we com-'elimates, is that known by the F-g' shpr pare the extreme temperatures of each month with anderes. These mountains of ine n the mean or normal temperatures of all the rest, we glaciers, properly so called, of S sha'l find — shores of Baffin's Bay. They detach from the general mass, with a mos thunder, when the waves have un teren base, and when the rap d een ze at in their fissures produces a sufficient expanu ite these huge misses and push them fi rwand exoses, and wich effects, we'l always read mus the range of human foresight.

That the mouth of Freury & Titti nes resemHes the mean secon! fortnight of April, or the mean first fortnight of January.

That the month of Mir å someti nes resembles the mean of the month of Apru, or the mean of the, second fortnight of January.

That the month of toeit never reaches the temperature of the mouth of May.

That the month of May is pretty frequently, in the mean, warmer than certa ǹ months of June. That the month of June is sometimes, in the men, warmer than certain months of July.

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That the morth of September is sometimes, in the mean, colder than certain months of October. That the month of Okriter may be, in the mean, nearly 3 (54 F.) colder than certain months of November.

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That the morth of December may be, in the m-an, 7′′ (12-6 F) coller than the month of Janwary.

DIST" REING CAUSES OF TERRESTRIAL TEMPERATURF
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