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Low o'er the grass the swallow wings,
HEIGHT OF CLOUDS.
The height of a cloud may sometimes be measured in the same manner as the height of any other inaccessible object, by simultaneous observations of its direction at two stations. More satisfactory results may, however, be obtained by ascending in a balloon, and noting the height of the barometer at the instant of entering a cloud, and again when emerging from it; thc barometer affording the means of computing the corresponding altitudes. In mountainous countries we may sometimes determine the height of a cloud by comparing it with some peak of known elevation near which the cloud is carried by the wind.
The height of clouds is very 'rariable, and their mean elevation is not the same in different countries. The stratus cloud often descends to the earth's surface. In pleasant weather, the lower limit of cumulus clouds varies from 3,000 to 5,000 feet elevation, and their upper limit from 5,000 to 12,000 feet. Cirrus clouds are never seen below the summit of Mount Blanc, which has an elevation of 15,744 feet.
Clouds are sometimes seen above the summit of Chimborazo, which has an elevation of 21,424 feet. Gay-Lussac and Glaisher, in their different balloon ascents to the height of 23,000 feet, saw cirrus clouds which appeared considerably above them. It is estimated that the greatest height at which visible clouds ever exist does not exceed ten miles.
CAN MAN ALTER THE WEATHER?
Sir John Herschel reasons out the subject thus conclusively in an article in Good Words of 1864 :
“ Is it in any degree within the power of man to alter the weather ? A strange question, it may seem at first sight, to propose ; but by no means so absurd a one as it may appear. The total rainfall, and, which is perhaps as regards weather and climate of even more importance, the frequency of showers on an extensive well-wooded tract, or one entirely covered by forests, ought, on every theoretical view of the causes which determine rain, to be greater than on the same tract denuded of trees. The foliage of trees defends the soil beneath and around them from the sun's direct rays, and disperses their heat in the air, to be carried away by winds, and thus prevents the ground from becoming heated in the summer ; while, on the other hand, a heated surface-soil reacts by its radiation on the clouds as they pass over it, and thus prevents many a refreshing shower, which they would others wise deposit, or disperses them altogether. So again of drainage :by carrying away rapidly the surface water down to the rivulet, and so hurrying it away to the ocean, it not only cuts off a great deal of the supply of local evaporation, which is a material element in the amount
of rainfall, but by causing the surface to dry more rapidly under the sun's influence, it allows it also to become more heated, and so to conspire with the action of the denudation of trees to prevent rain. Evidence is not wanting to corroborate this à priori view of the matter. The rainfall over large regions of North America is said to be gradually diminishing, and the climate otherwise altering, in consequence of the clearance of the forests; while, on the other hand, under the beneficent influence of a largely increased cultivation of the palm in Egypt, rain is annually becoming more frequent. Lakes are cited in what was formerly Spanish America (that of Nicaragua, if we mistake not is one), whose water supply (derived of course from atmospheric sources) had been so diminished, owing to the denudation of the country under the Spanish régime, as to contract their area and leave large tracts of their shores dry ; which, now that the vegetation is again restored, are once more covered by their waters. Even in our own southern counties complaints are beginning to be heard of a diminution of water supply, partly, it is said, owing to gradually decreasing rainfall from the universal clearance of timber, though chiefly perhaps attributable to robbing the springs of their supply by draining—a practice beneficial no doubt to agriculture, if used with caution and in moderation, but of which the consequences if carried to excess may ere long be severely felt, in rendering large tracts of country uninhabitable in summer from mere want of water."
METEORS AND AEROLITES.
A comparison of all the facts which are known respecting shooting. stars, detonating meteors and aerolites leads to the conclusion that they are all minute bodies revolving like the comets in orbits about the sun, and are encountered by the earth in its orbital motion. The visible path of aerolites is somewhat nearer to the earth's surface than that of ordinary shooting-stars, 2 result which may be ascribed to their greater density, which causes, therefore, greater resistance.
Th three classes of bodies exhibit alternate periods of maximum and minimum abundance, and the times of maximum for the several classes correspond somewhat with each other, indicating that these bodies are collected in groups, and the three classes of bodies are grouped in a somewhat similar manner, The August meteors move in orbits which require more than a century to complete, and comprehend bodies differing greatly in size and probably also in density. Their
magnitudes range from comets whose diameter is perhaps 100,000 miles to minute atoms which, in a single second, are dissipated by the heat resulting from their collision with our atmosphere. Their density ranges from that of metallic iron to earthy bodies having but feeble cohesion, which are dissipated into fine dust by the heat of collision with our atmosphere ; and it is possible that the rarest of them may consist of solid or liquid matter in a state of minute subdivision, like a cloud of dust or smoke.
The periodic meteors of November probably comprehend bodies having an equal range of magnitude, and perhaps also of density.Loomis.
THE LUNAR WEATHER THEORY.
The general principles of the lunar theory as to the weather are thus stated by Claudius Ptolemy, as quoted by Mr. A. J. Pearce in his “Weather Guide-Book,” according to Astro-Meteorology :
“The moon's course is to be carefully observed at the third day before or after her conjunction with the sun (new moon), her opposition (full moon), and her intermediate quarters ; for if she then shine thin and clear, with no other phenomena about her, she indicates serenity but if she appears thin and red, and have her whole illuminated part visible, and in a state of vibration, she portends winds from the quarter of her latitude and declination ;* and if she appear dark or pale and thick, she threatens storms and showers. All halos formed around the moon should also be observed, for if there appears one only, bright and clear, and decaying by degrees, it promises serene weather ; but if two or three appear, tempests are indicated ; and if they seem reddish and broken they threaten tempests, with violent and boisterous winds; if dark and thick they foreshow storms and snow; if pale, or black and broken, tempests with winds and snow, both; and whenever a great number appear, storms of greater fury are portended."
Sir John Herschel comments as follows on the theory
“Lunar prognostics about the weather may be classed under three several heads, namely :-1. Simple connotations of the appearance of
• Virgil says:
• Al si virgineum suffuderit ore ruborem,
Ventus erit: vento semper rubet aureu Phæbe."
halos, coronas, lunar rainbows, and a 'watery' moon, as prognostics of wet. No doubt they do indicate the presence of vapor passing into cloud in the higher regions of the air (in that of the rainbow, actual rain not far away), and so may be put on a par with the indications which may sometimes be gathered from the behavior of birds, especially such as fly and make long excursions, and which may convey to us some notion of their cogitations as to the coming weather, which are, perhaps, more likely to be right than our own, as founded on a wider range of perception. 2. Purely arbitrary laws or rules founded on the hour of the day or night at which the changes of the moon take place. There is (or was a few years ago, for we believe the race is dying out) hardly a small farmer or farm-laborer who had not some faith in certain 'weather tables' in the 'Farmer's Almanac,' ascribed (we need hardly say falsely) to the late Sir W. Herschel, and which went on this principle. Others, again, pressed into the service the great and recondite names of APOGEE (farthest from the earth), and PERIGEE (nearest to the earth), and professed to determine the character of the lunation from her proximity ai new or full to those mysterious points of her orbit. Both the one and the other rule utterly break down when brought to the test of long-continued and registered experience. Others, again, drew their prognostics for the whole lunation from the character of the weather during the first quarter. Such was the rule said to have been implicitly adhered to by the late Marshal Bugeaud in the planning of any military expedition whore success was likely to be any way dependent on weather :
Primus, secundus, tertius, nullus.
Tota luna talis. + 3. A more ambitious form of lunar prediction was that of the late eminent meteorologist (for such, this one crotchet excepted, he certainly was), Luke Howard, who took great account of the moon's declination as influencing the averages of rainfall and the height of the barometer. Still more so was his weather-cycle of nineteen years, the period of the circulation of the nodes of the moon's orbit ; in the course of which the absolute maximum of north declination occurs
The meaning of this Latin jumble seems to be that no indication can be deduced from the first, second and third days alone; that four days of any weather may be some indication; but that if any kind of weather last out for the first six days or 80, such will be that of the whole lunation.