"Un autre phénomène, qui parôit dans l'air, mériteroit bien qu'on s'étudiât à en découvrir la cause. Dans le tems le plus serein, on apperçoit tout à coup au milieu de la nuit de nuages d'une blancheur extraordinaire, et au travers de ces nuages une lumière très-éclatante. Lors même qu'on ne sent pas un souffle de vent, ces nuages sont chassés avec une très-grande vitesse, et prennent toutes sortes de figures. Plus la nuit est obscure, plus la lumière est vive: elle l'est même quelquefois à un point, qu'on peut lire à sa lueur beaucoup plus aisément, qu'à celle de la lune dans son plein.
"On dira peut-être que ce n'est qu'une réfraction des raïons du soleil, qui par cette hauteur ne s'éloigne pas beaucoup de l'horison pendant les nuits de l'été, et qu'encore qu'il n'y ait point de vent dans la basse région de l'air, il peut y en avoir dans la supérieure, ce qui est vrai; mais ce qui me fait juger qu'il y a encore une autre de ce météore, c'est que pendant l'hyver même, la lune paroît souvent environnée d'arc-en-ciel de couleurs différentes, et toutes très-vives. Pour moi je suis persuadé que ces effets doivent être attribués en partie à des exhalaisons nitreuses, qui pendant le jour ont été attirées et enfluencées par le soleil."
No. XXIV.
"Very distant posterity will one day decide whether, as Mr. Leslie has endeavored to prove by ingenious hypothesis (An Experimental Inquiry into the Nature and Propagation of Heat, 1804), 2400 years are sufficient to augment the mean temperature of the atmosphere a single degree. However slow this increment may be, we must admit that an hypothesis, according to which organic life seems gradually to augment on the globe, occupies more agreeably our imagination than the old system of the cooling of our planet and the accumulation of the polar ice."—Humboldt's Personal Narrative, vol. ii., p. 83.
"A point of much interest is the comparison of the actual temperature of the globe with that of the same regions in former ages. The evidence which justifies the conclusion that no change has occurred but from local or superficial causes, is worth studying, were it only for its variety and singularity. We might begin with Laplace's conclusion, that the mean heat can not be altered by 1° of Réaumur since the time of Hipparchus, inasmuch as the dimensions of the globe would be thereby changed in a small amount, its angular velocity be increased or diminished, and a sensible difference be made in the length of the day, which difference does not exist. We might then proceed to the argument urged by Biot and Champollion, from the identity of the time of inundation in the Nile, 5000 years ago, the periodical rains producing which depend upon and indicate the degree and distribution of heat over a vast equatorial region. Next we might turn to the method of Professor Schaw, in his work on the comparative temperature of ancient and modern times, founded on the northern and southern limits of production of different animals and plants in any given country, as they come recorded to us by ancient writers, compared with the observations of our own day. The result of general identity is obtained by this method also; and the same remark may be extended to the miscellaneous proofs derived from other passages in ancient writers, numerously collated, respecting the climate of particular regions and localities. There is no amount of diversity shown by this evidence which does not admit of explanation from local and accidental causes, many of them belonging to the agency of man himself, on the surface of the earth."—Quarterly Review, September, 1848.
"Several planters attribute the failure of the cotton crop this year (1842) to the unusual size and number of the icebergs, which floated southward last spring from Hudson's and Baffin's Bays, and may have cooled the sea and checked the early growth of the cotton plant, so numerous and remote are the disturbing causes of meteorology! Forty degrees of latitude intervene between the region where the ice-floes are generated and that where the crops are raised, whose death-warrant they are supposed to have carried with them."—Lyell's America, vol. i., p. 174.
No. XXV.
The theory by which Dr. Brewster seeks to account for the peculiarities of the American climate is the following: "He supposes that the poles of the globe and the isothermal poles are by no means coincident, and that, on the contrary, there exist two different points, within a few degrees of the poles, where the cold is greatest in both hemispheres. These points are believed by Dr. Brewster to be situated about the eightieth parallel of latitude, and in the meridians of 95° east and 100° west longitude. The meridians of these isothermal poles[223] he considers as lying nearly at right angles to the parallels of what might be called the meteorological latitudes, which, according to his theory, appear to have an obliquity of direction as regards the equator something like the zodiac. Thus the cold circle of latitude that passes through Siberia would be the same that traverses the frigid atmosphere of Canada. This theory would go some length toward explaining the causes of the gradual decrease of the severity of cold in the south of Europe, and lead us to the conclusion that eventually the cold meridian of Canada may work its way westward, and leave that part of America to an enjoyment of the same temperature as those European countries situated in corresponding latitudes. That the temperature of the air has been modified by agricultural operations can not be denied, but that these operations should of themselves be capable of producing the changes known to have taken place in the course of ages in Europe, where formerly the Tiber used to be often frozen, and snow was by no means uncommon at Rome;[224] when the Euxine Sea, the Rhone, and the Rhine, were almost every year covered with ice, of sufficient thickness to bear considerable burdens, it is scarcely possible rationally to admit; and, indeed, the meteorological observations, as far as they go in Canada, serve rather to disprove than to establish the fact."—Bouchette, vol. i., p. 335.
"The earliest record of the climate of Canada is that contained in the 'Fastes Chronologiques,' and refers to the period of Cartier's second voyage. On the 15th of November, 1535, Old Style, the vessels in the River St. Charles were surrounded by ice, and the Indians informed Cartier that the whole river was frozen over as far as Montreal. On the 22d of February, 1536, the River St. Lawrence became navigable for canoes opposite to Quebec, but the ice remained firm in the St. Croix harbor. On the 5th of April his vessels were disengaged from the ice. To obtain the modern dates, it will be necessary to add eleven days to each period.
"The later meteorological statistics do not prove that the progressive opening of the country has had so powerful an influence upon the temperature of the atmosphere as is generally supposed. Its chief tendency seems to be to lengthen the summer, and thus abridge the duration of winter. That the gradual removal of the forests to make room for open fields contributes to augment the summer temperature, is undoubtedly true, since it is well known that the atmosphere itself is not heated by the direct rays of the sun, but that its warmth springs from the earth, and that the degree of this warmth is entirely governed by the quantum of heat absorbed through the earth's surface. The progressive settlement of the country may then be expected to benefit the climate, by its throwing open to the direct action of the sun a more extended surface of territory; and this benefit will be more sensibly felt at night, from the earth's having imbibed a sufficient quantity of caloric to temper the coolness of the air between the setting and rising of the sun. In an agricultural point of view, such an improvement in the climate of Canada will be of great moment, as the coldness of the nights is generally the cause of blight in tender fruits and plants; and from its equalizing the temperature, probably render the climate capable of maturing fruits that are indigenous to warm countries.