ATMOSPHERIC PHENOMENA. II. Rain. "No water, no vegetables; no vegetables, no animals; no animals, no men." THE HE efforts of nature to maintain the proper balance of life by an adequate supply of water, are incredibly gigantic. Maury estimates that enough rain falls, annually, to cover the earth five feet in depth, or to form a belt three thousand miles wide and sixteen feet deep. The agent which lifts this immense mass is the sun's heat. The force exerted in making and raising the vapor from one acre has been calculated to equal the power of thirty horses; or for the whole area of the earth, a power eight hundred times greater than all the water-power of Europe.* The larger portion of the required moisture is manifestly-derived from the ocean and its tributaries; but there are other sources by no means unimportant. Hales ascertained that during twelve hours of daylight a sunflower yielded twenty ounces of vapor, and a cabbage nineteen ounces.† According to J. C. Draper, a man at rest exhales nearly three pounds per day of insensible perspiration; and Sanctoris asserts that in a heated or excited condition the amount rises to five pounds. For the conveyance of vapor we are indebted to the winds. The greatest extent of water surface is in the southern hemisphere, and there we find the greatest evaporation. But in the northern hemisphere the annual fall of rain exceeds that in the southern by about twelve inches. This can be accounted for only through the agency of the trade-winds. The southeast trade, laden with the burden of vapor from the southern seas, rises at the "Variables," crosses them, as we have already seen, and becomes the upper trade, blowing from the southwest. As it proceeds northward it becomes chilled, and at the calms of Cancer or the "horse latitudes," as navigators term them, it throws off a large portion of its moisture. To this wind northwestern Europe owes its rainy climate. CLOUDS. While suspended, the vapor is comparatively useless. It must fall. And here we come upon some of the most vexing problems in meteorology. It is easy to say with Tyndall that vapor becoming chilled condenses and falls as rain. But before the rain we have clouds. As these are simply collections of water-drops, or ice crystals, a difficulty presents "Phys. Geography of the Sea," p. 86. "Statical Essays," Lond., 1731, vol. 1, pp. 5 and 15. itself. How can water, specifically many times heavier than air, be sustained in the lighter element? With truly alchemistic subtilty, Descartes asserted that the vesicles of vapor are little spheres of water rendered buoyant by the materia subtilis of space. Dr. Franklin maintained that moisture is dissolved in the air as salts in water, and that when the particles are thrown off they hold their place by adhering to the atoms of air. Gay-Lussac refers their suspension to the impulsion of ascending currents of air; and Fresnel supposed that the solar heat absorbed by clouds forms groups of miniature Montgolfières, which rise according to their superior temperature. Mr. Rowell* recently offered a plausible explanation. In his estimation electricity is the controlling agency. "The atoms of water being so minute, are, when enveloped in their natural coatings of electricity, rendered so buoyant as to be liable, even in their most condensed state, to be carried off by slight currents of air; but if expanded by heat, their capacity for electricity being increased by their increase of surface, they are then rendered buoyant at all times, and are buoyed up into the air by their coatings of electricity; there, if condensed, they become positively electrified, but are still buoyed up by the electricity, till, on the escape of the surcharge, the particles fall as rain." The main objection to this hypothesis is its assumption that electricity is material, while, from analogy, we are led to believe that it, like heat and light, is merely a mode of motion. It is the most satisfactory, but any of the theories we have given may be taken with equal certainty, as "at present we do not possess sufficient data concerning the real constitution of clouds and the properties of the vapors, or the different elements which compose them, on which to ground a satisfactory explanation of their various appearances."+ To account for the precipitation of rain, another disputed matter, Mr. Rowell finds a ready cause in electricity. A particle, freed in some manner from its electrical coating, falls and coalesces with other particles to form drops. By the fall of these and the motion of discharged electricity, a vacuum is formed, and the sudden pressure to fill the space brings more particles into contact and produces more rain. Dr. Dalton held that if two masses of air of unequal temperatures are mixed when saturated with moisture, precipitation ensues; if they are under saturation there will be no precipitation, or if any, very slight. The action of electricity can only be secondary, the main cause is clearly reduction of temperature. The air may remain saturated for several days without a fall of rain, if the temperature is uniform; but a slight chilling of the atmosphere in such cases invariably produces rain. This is now the accepted theory of the formation of dew. It certainly applies with equal force to the formation of rain-drops. "An Essay on the Causes of Rain and its Allied Phenomena." Oxford. 1859. DISTRIBUTION OF RAIN. As has already been stated, rain is unequally distributed over the earth's surface. In some countries, near the equator and along the tropics, it rains almost incessantly during about one-third of the year, and is dry for the remainder. In other regions, showers are frequent at all seasons, but are of short duration; while in others it may be said never to rain. The advance of science has rendered these phenomena easy of explanation. In Ireland an umbrella is almost as essential as a hat. This country lies in the course of the southwest winds, which are merely the southeast trades. These convey the vapor from the southern seas, and also absorb, in their passage over the north Atlantic, much moisture, most of which is condensed by the headlands on the Irish coast. In Peru, west of the Andes, an umbrella is purely ornamental, and, in a lifetime, one might never luxuriate in a heavy shower. Peru lies in the region of perpetual southeast trade-winds. These cross the Atlantic and strike the coast of Brazil, over which they pass, depositing the vapor as they go, and at length reach the Andes, where their temperature is so reduced that the last particle of moisture is wrung out of them. They cross the mountains as dry winds, and receive no accession of vapor until they reach the Pacific. For like reasons we find rainless regions in Asia, Africa, and Western Mexico, These districts lie under the northeast trades, which, as the geography of the countries shows, are dry winds. The rainy seasons in tropical countries are caused by the motion of the trades as they follow the sun; at one season the trades prevail, and at another the surface winds, returning to the poles. In some districts lying on the weather-side of mountain ranges, the fall of rain is almost incredible. In Patagonia, where the northwest winds are literally desiccated by the Andes, Capt. King found the fall of water equal to nearly thirteen feet in forty-one days; and Darwin reports that the superficial sea-water along the coast is quite fresh.* Herschel says that nearly fifty feet of rain fall annually at Cherra Pungee.† ABNORMAL RAINS. Rains often contain ingredients other than water: Brine showers have occasionally fallen. One of these, which happened some years ago in Suffolk, England, incrusted the trees with salt, and rendered the grass so pungent that cattle would not eat it until forced by severe hunger. Dust storms are not unfrequent in volcanic countries, where also the rain often contains sulphurous acid. In our Western and Northern States, a yellow inflammable substance resembling sulphur sometimes accompanies rain. Naturalists regard this as the pollen of such plants as the alder and the "Maury, Phys. Geog. of the Sea," p. 98. 1 pine-trees which cover so large a portion of the Southern States. The most alarming of anomalous rains are the so-called blood-rains. Unfortunately, these have never been seen as they fell. In 1608, at Aix, the buildings were found sprinkled with great drops like blood, a phenomenon which produced great terror. The origin of these have never been determined, but they are usually regarded as the excrements of insects. In 1670, the people at the Hague awoke one morning to find their "lakes and rivers turned into blood." While the people were bemoaning their sins, a physician submitted some of the water to microscopical examination, and ascertained that the color was due to an animacule, the horned water-flea. Not less wonderful than blood-rains are frog-storms, which usually occur after protracted droughts. The frogs appear in vast numbers after the shower. Multitudes maintain that the animals are generated in the clouds, but there can be no doubt that the refreshing rain only revives the creatures and brings them from their holes. Such as have been seen in their fall, dropped under the eaves of houses, whence they had evidently been washed, as they were found in a sadly bruised condition. Signor Redi has shown that if the frogs fell from above there must have been green fields in the upper regions, for their stomachs contained herbs and other food half digested. Fish-storms are not uncommon, and are invariably accompanied by furious hurricanes. Such a storm occurred in a town not far from Paris, in France. It demolished many houses, but in measure recompensed the loss by strewing the streets with fine fish. The celestial origin of these was unquestioned until it was discovered that a well-stocked fish-pond, which stood on an eminence near at hand, had been blown dry. A hurricane once passed over Kent, England, and left the streets of one village deluged with rain and paved with sprats. After a long period of drought and scarcity in Silesia, there happened a providential shower of manna. As the peasants were about to gather plentifully and eat, a scientific man ascertained that the grains were seed of a species of veronica, set free from their pods by the rain. A similar occurrence took place at Warwick, England, in 1661, and the grateful people were offering their thanksgivings for the providential supply of wheat, when a committee of the Royal Society pronounced the "wheat" only seeds of ivy-berries conveyed thither by starlings.* ARTIFICIAL PRODUCTION OF RAIN. A problem of much practical importance, is the artificial production of rain. Among the Bechuanas there are rain merchants or doctors, who by incantations pretend to procure rain.† Dr. Livingstone and Winwood The greater number of cases here given have been selected from the "Encyclopedia Britannica" and an article in the "British Quarterly," 1859. "Moffat, Missionary Labors in South Africa." Amer. Ed., p. 209. Reade* give graphic accounts of the ceremonies observed by such impostors in Northern and Central Africa. Even in enlightened countries prayers to Divinities are supposed by some to be of avail. That rain could be obtained at will was a favorite theory of Arago. He had perceived that great battles are usually followed by heavy rainstorms, and therefore supposed that by repeated discharges of artillery the temperature of the atmosphere could be reduced below its dew-point. His experiments failed to substantiate the theory. Mr. Espy,† who, thirty years ago, was well known as an exceedingly independent thinker and investigator, maintained that in times of drought rain might readily be procured at any time. Having noticed that rain usually succeeds the burning over of woods or prairies, he conceived that if large fires were built in a circle inclosing a considerable area, rain might reasonably be expected soon after in the immediate vicinity. This theory met with much ridicule, but was so clearly borne out by facts, that its correctness is now generally conceded. The process recommended by Mr. Espy is too expensive, however, to come into general use, and practically the problem is still unsolved. HOWEVE DEMOCRACY IN EDUCATION. OWEVER men may differ with reference to democracy in government, there can be little hesitation on the part of any, who have passed through college, in denouncing it in the most cordial manner when applied to the management of an educational institution. Its effect in such cases is not to give all a chance to make progress according to their abilities, but to require all to make progress according to the limited abilities of some; or, in other words, to withhold from many the opportunities to which they are entitled. Industry and talent are robbed, while the standard of education is kept low. In the collegiate contest of mind with matter, brain with skull, the preponderance of power is given to those who have no claim to it. The requirements necessary for graduation-if these words may be so inaccurately employed-are adapted, with some degree of justice, to the most limited capabilities. But it is unjust that ability, which is beyond the average, should not be duly fostered and furnished with every advantage. The well-known circumstances are these. A class in college is composed of elements of the most heterogeneous description. In fact, it should be termed a congeries-not a class-since the latter term implies similarity on the part of those who constitute it. The Freshmen, however, are so unlike, that they never approximate throughout the whole of their course. "Savage Africa." Amer. Ed., p. 289. |