Which extend over the broadest region or greatest range of Are the trade-wind regions widest on the Atlantic or Pacific? this ocean? On the coast of what part of North America do periodical Do the hurricanes in various parts of the world generally have Does the region of the northern hemisphere in which south- Does that of the southern hemi sphere in which northwesterly winds predominate extend as In the middle and western part of what ocean does the ther- How much of the distance around the globe is it north of the NOTE. The specific causes of many of the facts to which attention is In which of these hemispheres is the course of the isothermal In what ocean do the isotherms of the north temperate latitudes Which sides, then, are the warmer within these limits? We have observed that the North Atlantic is warmer than the North Pacific; is the coast of Europe bordering the Atlantic likewise warmer than that of North America, in the same latitudes, bor- Is any part of the western coast of Europe obstructed in winter From the irregularity in the course of the isothermal lines in Which of the three great oceans has the widest space inclosed Do the isotherms extend farthest from the equator, on the by violent storms. 60, but varies with the seasons from 90 to 100. It is frequently interrupted "When the vessel on its voyage to the south approaches 439. The Zone of Culms, represented on the map, has a breadth of about breeze commences. during the night, and dies away in the morning when the seabreeze from the land, which blows freshly from off the coast o'clock it begins to subside, and is succeeded at evening by a the day, when it becomes a brisk gale; after two or three unequal heating of the land and sea. the shore, but gradually increasing in force till the middle of nine o'clock in the morning-at first blowing gently toward within the tropics, a breeze from the sea daily occurs about 437. Land and sea breezes are supposed to be caused by the the Brazil coast, from N. E. in the spring, and S. E. in autumn. September to March in the Gulf of Mexico. They occur also on Periodical currents, called nortes, or north-winds, blow from rope to Africa in summer is much quicker than the autumn. On the coasts and islands which carried her out. returning by a monsoon blowing in an opposite direction to that them a ship is frequently wafted to a distant port, and aided in and where do the nortes blow? breezes produced? 439. How wide is the Zone of Calms? caused? Describe them. 438. Where do these breezes prevail? How are regular inland effort the crew succeed in cutting through the remaining ropes, and the ship Questions.-436. What are the Etesian winds? Explain how they are caused. When A loud crack! a second, and the mainmast goes overboard! By a violent frightful roar; with a shriek the sails are torn asunder, and fly in ribbons! 487. How are land and sea breezes supposed to be flapping dismally upon the spars. Suddenly the storm bursts over with and rocks upon the irregular waves, but the sail still hangs against the mast, whence a streak of foam advances over the black ocean. The ship sways wall to the eastward; a low, shrill pipe resounds from the distance, from a peculiar coppery redness; and with the advancing night arises a black 440. The sun sinks below the horizon, the evening sky is illumined by the wild, murderous glance of despair. tongue to the palate. Each man looks upon his companion in suffering with spot. The store of water is exhausted. Glowing thirst glues the parched The deck burns through the soles of the shoes. cabins. A fortnight has the ruler of the sea lain immovable in the same glow through and through the narrow space in which the men are inclosed. lies bound on the crystal fluid. The rays of the sun, falling perpendicularly, glassy surface. The ship, hitherto speeding onward with a bird-like flight, little while, and at last drops entirely. Around extends the sea, an endless brought them thus far, becomes weaker and weaker; at first it ceases for a Sooner or later, according to the time of year, the favoring wind which had the equator in the midst of the Atlantic Ocean, anxious fear seizes the crew. A stifling vapor fills the snow-clad mountains, marshes, or sandy deserts. sphere, affected by the radiating properties of neighboring situations, are produced by changes in the density of the atmoinland breezes experienced in the morning and evening, in some nean and in the East and West India Islands. The regular from land. They are also very perceptible in the Mediterraof Malabar, where it is said that their influence is felt 60 miles 438. These breezes are particularly strong along the coast colder atmosphere of the north. Hence the passage from Euan almost vertical sun, and currents are created from the and flints, becomes very highly heated under the influence of of the Mediterranean, deprived of water, and composed of sand only throughout the day. The immense desert of Sahara, south ward the middle of July, about nine in the morning, and continue terranean, particularly the Levant, where they commence to from the northeast for about six weeks throughout the Medi436. The Etesian winas* are periodical winds which blow "Eros, a year, a season now flies over the ocean-now borne high upon the backs of the waves-now hurled down into the depths, so that every seam cracks and groans as though it would part asunder. The thunder rolls unceasingly; continuous lightning darts through the agitated atmosphere; the rain falls in streams instead of drops. Ten times the sailors give themselves up for lost, when the quaking bark falls into the trough of the sea, and as many times does it rise over the waves again. 441. "At last the storm lulls; single shocks follow, always at longer intervals; the waves become smoother, and when the consoling sun rises in the east, it illuminates the same dreary picture as on the former day. Mirror-like the endless surface again expands, and in eight days is the store of collected water exhausted; and again the silent specters creep about and turn murderous looks upon each other. A new storm, and a new calm, and so in frightful alternation, until at last the ship is driven into the region of the peaceful trade-wind on the other side of the equator. Hundreds of ships have gone down in storms here; hundreds lost their crews by the most frightful of deaths,-that of thirst; and those who have passed the fearful region of calms, turn in earnest worship to Heaven with thanks for their new-won life."0 LESSON VI. HURRICANES. 442. THE terms hurricane, whirlwind, water-spot, land-spout, sand-pillar, tornado, white squall, pampero, etc., have been ap the southern hemisphere their rotation is direct, conformable to the hands of a watch. 445. There are three well-known hurricane regions-the West Indies, the Indian Ocean, and the China Sea. The general course of the West Indian hurricanes is from the Leeward Islands N. W., passing around the shores of the Gulf of Mexico or across it, then following the Gulf Stream and terminating in the Atlantic, or exhausting their fury in the United States. From October 3, 1780, to August 25, 1837, inclusive, 38 hurricanes occurred in this region in the following months in June, 1; July, 4; August, 13; September, 10; October, 8; exclusive of two, the months of which have not been recorded. Thus they are very rare in June, and most frequent in August. The only instance in June occurred in 1831, when Trinidad, Tobago, and Grenada were devastated, before supposed to be exempt from hurricanes. 446. The hurricanes of the Indian Ocean come from the N. E., near Sumatra and Java, and travel to the S. W. toward Rodriguez and the Mauritius. They occur chiefly from December to April, the hot season in that hemisphere; are very rare in November and May; and are quite unknown during the other months of the year. 447. In the China Sea, hurricanes, there styled typhoons, range from 10° to 30° N. They occur from June to November, after an interval of three or four years. plied to rotary movements of the atmosphere in different parts of the world. 443. Hurricanes are revolving storms which occur chiefly in the West Indies and in the Indian Ocean. Of a similar kind are the typhoons in the China Sea. These circulating movements occupy a space from 50 to 500 miles in diameter. They revolve the more rapidly the nearer the center, up to a certain distance, within which there is a calm. 444. The center of rotation advances steadily along a definite line upon the globe, with a velocity varying from 2 to 30 or 40 miles per hour. It is a remarkable fact, that in the same hemisphere these whirling storms always revolve the same way, but that this direction is opposite in opposite hemispheres. In the northern hemisphere their rotation is retrograde, or in a direction opposite to the hands of a watch. In Questions.-442. What terms have been applied to the rotary movements of the atmosphere? 448. What are hurricanes? What space do these circulating movements occupy? Where do they revolve the more rapidly? 444. What is the velocity of the center of rotation? What is a remarkable fact? What is the rotation of the storms in the northern hemisphere? In the southern hemisphere? 445. Which are the three wellknown hurricane regions? Schleiden's "Lecture about the Weather." LESSON VII. MOISTURE. 448. IF we place a vessel of water in the open air on a warm day, the quantity of the fluid will soon be sensibly diminished, or evaporated, being converted by the heat into invisible vapor, and diffused through the air. In like manner evaporation transpires upon a grand scale from the great collections of water on the earth's surface, the oceans, lakes, and rivers, as well as from moist ground. It is subject to diurnal and annual variations. 449. The quantity of vapor diffused through the air is least in the morning before sunrise. As the temperature rises with the ascent of the sun, evaporation increases. The heat of mid Questions.-What is the general course of the West Indian hurricanes? When are hurricanes in this region most rare, and when most frequent? 446. Describe the hurricanes of the Indian Ocean. When do they chiefly occur? 447. What is said of the typhoons? When and how often do they occur? 448. What will happen if we place a vessel of water in the open air on a warm day? Where does evaporation transpire on a grand scale? 449. When is the quantity of vapor diffused through the air the least? When does evaporation increase? What does the heat of mid-day cause? In what month is the quantity of vapor at its minimum, and in what at its maximum? day causes the vapors to rise into the upper regions, and hence the greatest degree of dryness is generally felt during the daytime, though evaporation is then going on most rapidly. In January the quantity of vapor, like the mean temperature of the air, is at its minimum: it increases from that period, and in July attains its maximum; it then decreases to the end of the year. 450. The moisture in the atmosphere is an element on which the life of plants and animals as much depends as on temperature. The healthfulness of climate is greatly influenced by the dryness or humidity of the atmosphere. As resulting from the action of heat on water, the quantity of vapor diminishes with the temperature from the equator to the poles. It decreases also as we pass from coasts into the interior of continents. This rule is confirmed in the interior of the United States, in the middle of the plains of the Orinoco, in the steppes of Siberia, the deserts of Asia and Africa, and the central parts of Australia. In the temperate zone, in general, the annual evaporation is estimated at between 36 and 37 inches of water. In the torrid zone, at Guadaloupe, it has been found to amount to 97 inches, and at Cumana to 100 inches. 451. The air is only capable of receiving a certain quantity of vapor. Its capacity depends upon its temperature, and is invariable in its extent at the same temperature. According to Professor Leslie, air at the freezing point is capable of holding moisture equal to the 160th part of its own weight; at the temperature of 59°, the 80th part; at that of 86°, the 40th part; at 113°, the 20th part; and at that of 140°, the 10th part. 452. When a volume of air contains as much aqueous vapor as at its particular temperature it is capable of receiving, it is then said to be at the point of saturation, being as humid as can be. If the temperature then rises, it will be capable of receiving more; but if it falls, some of the contained vapor will be rejected, and become visible as mist. Thus the effect of a change of temperature upon a saturated volume of air is analogous to that of the hand relaxing or tightening its grasp on a piece of imbibing sponge. 453. It has been frequently observed that the summits of some mountains are constantly covered with clouds. The formation of such clouds may be thus explained: The winds, laden with vapor from lower and warmer districts, in passing over such ranges are forced up into a colder region, where they are obliged to part with a portion of the vapor, which thus forms a cloudy state of the atmosphere. 454. Mists and fogs are formed when the air is saturated, and generally when the moist soil, or the water of lakes and rivers is warmer than the air, the vapors of which are immediately condensed. In like manner the vapor of the air breathed from our mouths in winter becomes condensed and visible. Mists differ in no respect from clouds except in position, being on the surface of the earth, instead of being suspended at a height in the atmosphere. 455. The thick mists which prevail in the neighborhood of Newfoundland Questions.-450. What is said of the moisture in the atmosphere? How does the quantity of vapor diminish? Annual evaporation in the temperate zone? In the torrid zone? 451. What is said of the capacity of air for receiving vapor? Upon what does it depend? Give its capacity at different states of temperature. 452. When is a volume of air said to be at the point of saturation? 458. What has been frequently observed? How may the formation of such clouds be explained? 454, When are mists and fogs formed? How do mists differ from clouds? 457. Dew is formed by the gradual condensation of the vapors of the atmosphere. After sunset in summer, when the great diurnal evaporation has filled the air with moisture, and the earth is gradually cooled by radiation under a clear sky, the atmosphere in contact with the surface is chilled, and has its capacity to retain the aqueous vapors lessened, which are gradually and gently deposited in the form of fluid drops, called dew. In some countries dew supplies the place of rain. In Palestine and western Asia in general, where showers are unknown for several months in succession, the dew formed at night moistens the earth and sustains the vegetation, being often so abundant as completely to saturate the tents, baggage, and clothing of travelers exposed to it. 458. As all objects have not the same capacity for radiating heat, some cooling much more rapidly than others, we frequently find certain bodies densely covered with dew, as grass and leaves, while the bare grounds, metals, stones, and wood are comparatively dry. A thermometer laid on a grass-plot on a cloudless night has been upward of 16° lower than another. laid at the same time on a gravel walk. Hence there has been a much more copious deposition of dew on the grass than on the walk,—the herbs needing the nourishment thus receiving it in preference to the bare soil-a striking evidence of an allwise Being operating in the economy of nature.* LESSON VIII. CLOUDS. 459. CLOUDS are masses of visible vapor like mists, floating in the atmosphere at a distance from the surface of the earth. Questions.-455. Origin of the mists which prevail in the neighborhood of Newfoundland? 456. Explain why mists are frequently formed over the beds of lakes and rivers while the adjacent land is free from them. 457. How is dew formed? Explain particularly the operation of its formation. What is said of the dews of Palestine and western Asia? 458. Why does dew collect more on some bodies than others? 459. What are clouds? What is said of them? * Rev, Thomas Milner. 1, 1. Cirrus. 3. Cumulus. 5. Stratus. 2 2. Cirro-Cumulus. 4. Nimbus. clouds are usually formed toward noon, when the vapors are raised up by the ascending currents of air, and then condensed by the lower temperature of the upper regions. 460. Though clouds are generally composed of vapor, they may consist of frozen particles. In winter, during severe cold, we can often observe that the vapors which rise are composed of brilliant needles, that glisten in the sun and resemble small flakes of snow. The same thing must take place in the higher regions of the atmosphere. There exist, therefore, snowclouds and clouds of vapor of water. 461. Notwithstanding the varied aspect of clouds, they may be arranged into three principal classes-the cirrus, the cumulus, and the stratus. 462. Cirrus Curlcloud. Fig. 1.-The cirrus (the cat's-tail of sailors) is composed of thin filaments, variously disposed, in the form of woolly hair, a crest of feathers, or slender net-work. The cirri appear in the higher regions of the atmosphere, and are the most elevated of the clouds. Viewed from the summits of high mountains, while the traveler looks down upon other forms of clouds, he beholds these still above him, and apparently at as great a distance as when seen from the plains. The appearance of true cirrus, or curlcloud, is supposed to indicate variable weather; when most conspicuous and abundant, to presage high winds and rain; and when the streaming Questions.-460. Of what are clouds composed? What two kinds? 461. Into what three principal classes may clouds be arranged? 462. Describe the cirrus or curlcloud. What is said of the height of the cirri? What is the cirrus supposed to indicate? 463. Describe the cumulus or stackencloud. Of what does it consist? fibers have pointed in a particular direction for any length of time, the gale may be expected to blow from that quarter. 463. Cumulus-Stackencloud. Fig. 3.-This form of cloud (ball of cotton of sailors) occurs in the lower regions of the atmosphere, and is easily recognized. It is commonly under the control of the surface winds, and frequently exhibits a very magnificent appearance. It consists of a vast hemispherical or conical heap of vapor rising gradually from an irregular horizontal base and increasing upward. Hence the names cumulus, a pile or heap, and stackencloud, a number of detached clouds stacked into one large and elevated pile. 464. Cumuli are indications of fine weather. They begin to form soon after sunrise from irregular and scattered specks of cloud; as the morning advances the clouds enlarge; and early in the afternoon, when the temperature of the day is at its maximum, the cumulus attains its greatest magnitude. The cloud decreases as the sun declines, and is usually broken up toward sunset. The cumulus may be called the cloud of day, from the interval between morning and evening generally measuring the term of its existence. Its appearance considerably varies in the detail, and often exhibits a brilliant silvery light, and a copper tinge, when in opposition to the sun, indicating a highly electrical condition of the atmosphere. 465. Stratus-Fallcloud. Fig. 5.-This cloud consists of horizontal bands near the surface of the earth. It belongs to the night, forming at sunset and disappearing at sunrise. This class of clouds comprehends all those fogs and creeping mists which sometimes spread like a mantle over the surface of the valleys, plains, lakes, and rivers. 466. To the above primary varieties three transition or composite forms are added. Cirrocumulus-Sondercloud. Fig. 2. This name designates the feathery accumulated cloud, familiarly known as fleecy, intermediate between cirrus and cumulus. Wanecloud and Cumulostratus-Twaincloud (not represented in the cut), are combinations, the former of the cirrus and stratus, and the latter of the cumulus and stratus. 467. Nimbus-Raincloud. Fig. 4.-Any of the preceding modifications may pass over into the actual rainy clouds, first exhibiting a great increase of density, and a bluish-black tone of color, then putting on a lighter shade, or gray obscurity, and becoming fringed at the edges. 468. Clouds are generally higher within the tropics than in the temperate zones; and in the temperate zones they are commonly higher in summer than in winter. The cirri are the highest clouds. They are supposed to range from three to five miles above the level of the earth. Kaemtz states that during a stay of eleven weeks within sight of the Finsteraarhorn, upward of 14,000 feet high, he never observed any cirri below the summit of the mountain. It is highly probable that they consist of flakes of snow. 37 313 44 343 66 Annual quantity of rain within the tropics of the New World..115 inches. Annual quantity of rain in the temperate zones of the New World (United States)..... In the temperate zones of the Old World (Europe)... 473. Although the amount of rain is greater within the tropics than in the temperate zones, yet the number of rainy days is less, because two seasons divide the year-wet and dry; and during the dry season entire months frequently pass away without a drop falling or a cloud being seen. In the temperate zones, also, in passing from the tropics to the polar circles, the number of rainy days increases, although the intensity of rain diminishes. Annual number of rainy days in North of Syria..... 54 LESSON IX. RAIN. 469. RAIN is water, which, originally taken up into the atmosphere in the state of vapor, is returned to the earth in the form of liquid drops. It is produced by the continued condensation of vapor. Rain may begin to fall, and yet not reach the ground, being resolved into invisible vapor on arriving at strata of air removed from the point of saturation. For the same reason, rain-drops may become smaller in their descent, a portion being evaporated, and less rain arrive at the earth's surface than at a certain height above it. Usually the drops increase in their fall, bringing with them the low temperature of the upper regions. 470. The following are examples of very extraordinary showers : 1822-Oct. 25, at Genoa, 30 inches of rain fell in 24 hours. 1827.-May 27, at Geneva, there fell 6 inches of rain in 3 hours. 1841.-June 4, at Cuiseaux, a small town in the valley of the Saone, there fell about 11 inches in 68 hours. At Cayenne, Admiral Roussin collected 10 inches in 10 hours. 471. Rain is very unequally distributed over the regions of the globe. 1. The average annual quantity of rain is the greatest in tropical climates, and diminishes as we recede from the equator to the poles. 2. It decreases as we pass from maritime to inland countries, because the land supplies a less quantity of vapor than the sea. 3. More rain falls in mountainous than in low level districts, lofty heights arresting the clouds, and promoting the condensation of vapor by their cold summits. 4. The result of experiment shows that a greater amount of rain falls while the sun is below than when above the horizon. 472. The diminution of the average annual quantity of rain from the equator to the poles, appears from the following table: San Luis de Maranhao.. ..lat. 30 S. is equal to 276 inches. Parimaribo, "60 N. Guiana. 66 229 66 Questions.-467. Change to the nimbus or rain-clond? 469. What is the comparative height of clouds in different zones and seasons? Height of the cirri? What does Kaemtz state? 469. What is rain? How produced? 470. Give examples of very extraordinary showers. 471. What is said of the un qual distribution of rain? Where is the average annual quantity the greatest? Where does it decrease? What is observed of mountainous distris? What does the result of experiment show? 472. What is the annual quantity of rain in different places? The annual quantity within the Tropics of the Old World? Of the New World? Average for the Tropics generally? Annual quantity in the Temperate Zones of the New World? APPROACHING STORM. SAMBRO LIGHT ENTRANCE TO HALIFAX HARBOR. 474. Countries situated in the vicinity of the sea receive, as we have remarked, a larger amount of rain than those inland. This is exemplified in the interior of the United States, of the Llanos of the Orinoco, of the Siberian steppes, of Australia, and on comparing the amount of precipitation in inland and maritime countries. It declines from an annual fall of between 30 and 35 inches on the shores of Great Britain and France to from 15 to 13 inches as the borders of Asia are approached. Mountains produce several exceptions to this rule. The annual number of rainy days de creases also with the increased distance from the sea. Questions. In the Temperate Zones of the Old World? In the Temperate Zones general y? 478. Where is the number of rainy days less than in the Temperate Zones, and why? What is observed in passing from the Tropics to the polar circles? State the annual number of rainy days in different places? 474. What is said of countries situated in the vicinity of the sea? How is this exemplified? With what does the annual number of rainy days decrease? Illustrate. 475. What facts illustrate the difference between mountainous districts and low and level countries with respect to the fall of rain? What is remarked of the description of Judea, by the seared writer 1 |