Physical Geography of the Sea and its Meteorology/Chapter 21
CHAPTER XXI.
§ 850-880.—THE ANTARCTIC REGIONS AND THEIR CLIMATOLOGY.
850. Indications of a mild climate about the south pole.—During our investigations of the winds and currents, facts and circumstances have been revealed which indicate the existence of a mild climate— mild by comparison— within the antarctic circle. These indications plead most eloquently the course of exploration there the facts and circumstances which suggest mildness of climate about the south pole are these: a low barometer, a high degree of aerial rarefaction, and strong winds from the north.
851. The story of the winds.—The winds were the first to whisper Of this strange state of things, and to intimate to us that the antarctic climates are in winter very unlike the arctic for rigour and seventy. In dividing the sea into wind-bands (§ 8522) or longitudinal belts 5° of latitude broad each, I excluded from the table on the next page, observations from those parts of the sea, such as the North Indian Ocean, the China Sea, and others where monsoons prevail. The object of this exclusion was to investigate the general movements of the atmosphere, hence the propriety of excluding all regions which are known to present exceptional cases to the general law. The grouping was not carried beyond lat. 60° north and south, for the lack of observations on the polar side of those parallels. The number of observations thus becoming available was 1,159,353. These were then divided simply into two classes for each belt, viz., polar winds[1] and equatorial winds. They were then reduced to terms of a year, and the average prevalence of each wind in days deduced therefrom, as per Plate XV., and the following table:—
Polar and Equatorial Winds.
| Belts. | Northern Hemisphere. | Southern Hemisphere. | ||||||||
| No. of Observations. | Equatorial. | Polar. | Excess in Days. | No. of Observations. | Polar. | Equatorial. | Excess in Days. | |||
| Days. | Days. | Equatorial | Polar. | Days. | Days. | Polar. | Equatorial, | |||
| Between | ||||||||||
| 0°and 5° | 67,829 | 79 | 268 | .. | 189 | 72,945 | 83 | 269 | .. | 186 |
| 5 ,, 10 | 36,841 | 158 | 183 | .. | 25 | 54,648 | 72 | 283 | .. | 211 |
| 10 ,, 15 | 27,339 | 278 | 73 | 205 | .. | 43,817 | 82 | 275 | .. | 193 |
| 15 ,, 20 | 33,103 | 273 | 91 | 182 | .. | 46,604 | 91 | 266 | .. | 175 |
| 20 ,, 25 | 44,527 | 246 | 106 | 140 | .. | 66,395 | 128 | 227 | .. | 99 |
| 25 ,,30 | 68,777 | 185 | 163 | 22 | .. | 66,635 | 147 | 208 | .. | 61 |
| 30 ,, 35 | 62,514 | 155 | 195 | .. | 40 | 76,254 | 150 | 204 | .. | 54 |
| 35 ,,40 | 41,233 | 173 | 179 | .. | 6 | 107,231 | 178 | 178 | 0 | 0 |
| 40 ,,45 | 33,252 | 163 | 186 | .. | 23 | 63,669 | 202 | 155 | 47 | .. |
| 45 ,, 50 | 29,461 | 164 | 189 | .. | 25 | 29,132 | 209 | 148 | 61 | .. |
| 50 ,,55 | 41,570 | 148 | 203 | .. | 55 | 14,286 | 208 | 151 | 57 | .. |
| 55 ,, 60 | 17,874 | 142 | 213 | .. | 71 | 13,617 | 224 | 132 | 92 | .. |
852. The null belts.—This plate and table reveal a marked difference in the atmospherical movements north, as compared with the atmospherical movements south of the equator. The equatorial winds of the northern hemisphere are in excess only between the parallels of 10° and 30°; i. e., they are the dominant winds over a zone 20° of lat. in breadth, while the equatorial winds of the southern hemisphere hold the mastery from 35° S. to 10° N.; i. e., they are the dominant winds over a zone 45° of lat. in breadth, while the others cover a space not half so broad. This table, moreover, shows the debatable ground between the winds, or what may be called the null belt in this general movement from poles towards the equator, and from equator towards the poles, is, in the northern hemisphere, between the parallels of 25° and 50°. In the southern the field of battle is narrowed down to a single belt (between 35° and 40°); here the two winds exactly counterbalance each other. As the seaman proceeds from this medial belt, the winds increase belt for belt very nearly pari passu on the polar side, the polar winds—on the equatorial, the equatorial winds, gaining more and more in days of annual duration, and more and more in average velocity each.
853. Extent of the polar indraught.—The fact that the influence of the polar indraught upon the winds should extend from the antarctic to the parallel of 40° S., while that from the arctic is so feeble as scarcely to be felt in 50° N., is indicative enough as to difference in degree of aerial rarefaction over the two regions. The significance of this fact is enhanced by the "brave west winds," which, being bound to the place of greatest rarefaction, rush more violently and constantly along to their destination than do the counter-trades of the northern hemisphere. Why should these polar-bound winds of the two hemispheres differ so much in strength and prevalence, unless there be a much more abundant supply of caloric, and, consequently, a higher degree of rarefaction, at one pole than the other?
854. The rarefaction of the air over polar regions.—In the southern hemisphere—and our attention is now directed exclusively to that—the polar winds on the south side of 40° are very much stronger than are the equatorial winds on the north side of 35°: a fact indicative of a greater degree of rarefaction about the place of polar calms than we have in the equatorial calm belt.
855. Barometrical observations.—That such is the case is also suggested by the fact that the indraught into the antarctic calm place is felt (§ 854) at the distance of 50° from the pole all round, while the equatorial indraught is felt no farther than 35° from the equator; and that such is the case is proved by the barometer. Lieutenant Andrau, of the Meteorological Institute of Utrecht, has furnished us from the Dutch logs with 83,334 observations on the height of the barometer between the parallels of 50° N. and 36° S. at sea. Lieutenants Warley and Young have extracted from the log-books in the Washington Observatory, taken at random, 6,945 observations on the barometer south of the parallels of 40° at sea. Dr. Kane has furnished us with the mean height of the barometer in lat. 78° 37' N., according to 12,000 hourly observations made during his imprisonment of 17 months in the ice there. The annals of Greenwich at St. Petersburg give us the mean height of the barometer in lat. 51° 29' N., according to three years' observations, and in lat. 59° 51' N., according to ten years of observation. Such are the sources of the table.
Mean Height of the Barometer
| Latitude. | Barometer. | No. of Observations. |
Latitude. | Barometer. | No. of Observations. |
| 0° to 5° N. | 29.915 | 5114 | 0° to 5°S. | 29.940 | 3692 |
| 5 ,, 10 | 29.922 | 5343 | 5 ,, 10 | 29.981 | 3924 |
| 10 ,,15 | 29.9(54 | 4496 | 10 ,, 15 | 30.028 | 4156 |
| 15 ,,20 | 30.018 | 3592 | 15 ,, 20 | 30.060 | 4248 |
| 20 ,,25 | 30.081 | 3816 | 20 ,, 25 | 30.102 | 4536 |
| 25 ,,30 | 30.149 | 4392 | 25 ,, 30 | 30.095 | 4780 |
| 30 ,, 35 | 30.210 | 4989 | 30 ,, 36[2] | 30.052 | 6970 |
| 35 ,, 40 | 30.124 | 5103 | 40 ,, 43 | 29.88 | 1703 |
| 40 ,, 45 | 30.077 | 5899 | 43 ,, 45 | 29.78 | 1130 |
| 45 ,, 50[2] | 30.060 | 8282 | 45 ,, 48 | 29.63 | 1174 |
| 51° 29' | 29.814[3]> | Greenwich | 48 ,,50 | 29.62 | 672 |
| 59° 51' | 29.88 | St. Petersburg | 50 ,, 53 | 29.48 | 665 |
| 53 ,,55 | 29.36 | 475 | |||
| 78° 37' | 29.759 | Dr. Kane | 56½ | 29.29 | 1126 |
856. The low austral barometer.—Captain Wilkes, U. S. N., and Clarke Ross, R.N., both, during their expeditions to the South Seas in 1839-41, had occasion to remark upon the apparent deficiency of atmosphere over the extra-tropical regions of the southern hemisphere; and the low barometer off Cape Horn had attracted the attention of navigators at an early day. I observed it in 1831 when doubling the Cape as master of the U.S.S. "Falmouth," and wrote a paper on it, which was published in the American Journal of Science in 1833-4. The more abundant materials which the abstract logs since placed within my reach have enabled me to go more fully into this subject than it was possible to do while I was cruising in the Pacific more than a quarter of a century ago. To ascertain whether these "barometric anomalies," as they are called, are peculiar to the regions about Cape Horn, or whether they are common to high southern latitudes in all longitudes, the observations about Cape Horn were arranged in one group; those between 20° W. and 140° E. in another; and those between 140° E. and 80° W. in another, with the following results:—(They are all on the polar side of lat. 40° S.)
Mean Height of the Barometer, as observed between
| The parallels of | The Meridians of | |||||||
| 20° W. & 140° E. | 140° E. & 80° W. | Off Cape Horn. | Mean of all. | |||||
| No. of Observations | Barometer Inches. | No. of Observations | Barometer Inches. | No. of Observations | Barometer Inches. | No. of Observations | Barometer Inches. | |
| 40° S. and 43° S. | 1115 | 29.90 | 210 | 29.84 | 378 | 29.86 | 1703 | 29.88 |
| 43 ,, 45 | 738 | .80 | 155 | .73 | 237 | .75 | 1130 | .78 |
| 45 ,, 48 | 611 | .58 | 226 | .71 | 337 | .68 | 1174 | .63 |
| 48 ,, 50 | 175 | .53 | 247 | .56 | 250 | .61 | 672 | .62 |
| 50 ,, 53 | 108 | .35 | 198 | .45 | 359 | .56 | 665 | .48 |
| 53 ,, 55 | 6 | .17 | 92 | .35 | 377 | .37 | 475 | .36 |
| S. of 55° | 7 | .27 | 64 | .42 | 1055 | .28 | 1126 | .29 |
857. Discussion of observations.—The instruments used for these observations were for the most part the old-fashioned marine barometer, to which no corrections have been applied. The discrepancies of this table evidently arise from the lack of number sufficient to mask these sources of error, or from the influence of the land, and not from any difference as to the mean height of the barometer along the same parallels at sea in any one of the three divisions. In this discussion, the observations of each group and every band were arranged according to the month. These monthly tables are not repeated here, but they do not indicate any decided change in the barometric pressure in high southern latitudes according to the season. The barometer there stands low the year round.
858. Barometric curve at sea.—Resorting to the graphic method and using the table (above) for the purpose, the barometric curve of the diagram (Plate XVI.) has been projected from pole to pole.
859. Ditto over the land.—Professor Schouw has given us the mean height of the barometer for 32 places on the land between the parallels of 33° S. and 75° 30' N. They afford materials for the annexed diagram, and show the exceptional character of the meteorological influences which rule on shore when compared with those which rule at sea. There is barely a resemblance between this profile of the atmosphere over the land and the profile of it (Plate XVI.) over the sea, so different are these influences.
860. Agreement of observations at sea.—The diagram (Plate XVI.) shows the observations in the southern hemisphere to be so accordant, and the curve itself so regular, that we feel no hesitation about projecting this curve into the unexplored spaces of the south, and asserting, with all the boldness consistent with the true spirit of philosophical deduction, that, whether the actual barometric pressure at the south pole be as low as 28.14 or not, it is nevertheless very much lower in the antarctic than in the arctic regions.
861. The question why the barometer should stand lower about the south than the north pole considered.—The question now arises, Whence this unequal distribution of atmosphere between the two hemispheres, and why should the mean height of the barometer in circumpolar regions be so much less for the austral than for the boreal? No one, it is submitted, will attempt to account for this difference by reason of any displacement of the geometrical centre of the earth with regard to its centre of attraction, in consequence of the great continental masses of the northern hemisphere; neither can it be ascribed to any difference in the forces of gravitation arising from the oblateness of our globe; neither can it be accounted for by the effects of diurnal rotation after the Halleyan theory: that would create as low a barometer at one pole as the other. The air, in its motions to the east and in its motions to the west, is in equipoise between the parallels of 35° and 40° N., 25° and 30° S. There is near each pole and about the equator a place of permanently low barometer. The air from all sides is continually seeking to restore the equilibrium by rushing into those places of rarefaction and reduced pressure; consequently there ought to be between each pole and the equator a place of high barometer from which the air on one side flows towards the equator, on the other towards the pole. Observation (p. 455) shows this high place to be between the parallels of 25° and 40° in the north, and of 20° and 30° in the southern hemisphere: thus the barometer as well as the winds, Plate XV., are both indicative of a greater degree of rarefaction about the south than about the north pole. Were there no friction, and were the atmosphere ordained to move without resistance, the air from these null belts would carry with it to the polar calms the easterly motion which it had acquired from the earth in its motion around its axis at these null belts. Were this motion so impressed, the wind would arrive, rushing with an hourly velocity about the polar calm places of 700 miles in the arctic, and 800 in the antarctic. Such a velocity would impart a centrifugal force sufficient to keep the air away from the poles and produce almost a vacuum there. In this state of things, the same air would continue to revolve about the poles were not some other agent, such as heat, brought in to expand and drive it away. Being expanded and puffed out above the general atmospherical level, but retaining its velocity—for the supposition is that it moves without friction—and returning through the upper regions, it would flow back as it went, viz., as a westerly wind, and arrive at its null belt in the direction of the meridian. But the wind has friction, and is resisted in every movement; the atmosphere partakes of the spheroidal form, which has been impressed upon the earth itself by its axial rotation. That form is to it the form of stability. The water at the pole is about 13 miles nearer to the centre of the earth than the water at the equator; but there is not on that account any tendency in the sea to flow back from the equator towards the poles; neither is there any tendency to motion one way or the other in the atmospherical ocean by reason of the oblateness of its surface. To produce the polar and equatorial movements of the air, there must be an agent both at the equator and the poles to prevent such stability by constantly disturbing equilibrium there, and that agent is heat; therefore, whatever be the degree of depression due the polar barometer in consequence of axial rotation, such depression could, of itself, produce neither trade nor counter-trade wind; it could no more produce currents in the air than in the sea, nor could axial rotation produce a high barometer at one pole, a low barometer at the other; consequently, the difference in the pressure of the atmosphere about the two poles, as shown by the diagram (Plate XVI.), cannot be ascribed to the influence of axial rotation. It is doubtless due to the excess in antarctic regions of aqueous vapour and its latent heat.
862. Psychrometry of polar winds.—The arctic circle lies chiefly on the land, the antarctic on the water. As the winds enter one, they are loaded with vapour; but on their way to the other they are desiccated (§826). Northern mountains and the hills wring from them water for the great rivers of Siberia and Arctic America. These winds, then, sweep comparatively dry air across the arctic circle; and when they arrive at the calm disc—the place of ascent there—the vapour which is condensed in the act of ascending does not liberate heat enough to produce a rarefaction sufficient to call forth a decided indraught from a greater distance in the surrounding regions than 40° (§ 852)—2400 miles; and the rarefaction being not so great, the barometer is not so low there as in antarctic regions.[4]
863. Aerial rarefaction about the north pole.—Nevertheless, there is rarefaction in the arctic regions. The winds show it, the barometer attests it, and the fact is consistent with the Russian theory of a polynia in polar waters. The presence within the arctic circle of a considerable body of comparatively warm water, which observation has detected going into it as an under current—which induction shows must rise up and flow out as a surface current—would give forth vapour most freely. This vapour, being lighter than air, displaces a certain quantity of atmosphere. Rising up and being condensed, it liberates its latent heat in the cloud region, and so, by raising temperature, causes the moderate degree of rarefaction which the barometer at sea, at Greenwich, at St. Petersburg, and in the arctic ice indicates.
864. Ditto about the south pole.—Within the antarctic circle, on the contrary, the winds bring air which has come over the water for the distance of hundreds of leagues all around; consequently, a large portion of atmospheric air is driven away from the austral regions by the force of vapour, which fills the atmosphere there. Now there must be a place—an immense disc, with irregular outlines, it may be, and probably is—where these polar winds (§ 855) cease to go forward, rise up, and commence to flow back as an upper current. If the physical aspects—the topographical features in and about this calm place—be such as to produce rapid condensation and heavy precipitation (Chap. XX.), then we shall have, in the latent heat liberated from all this vapour, an agent sufficient not only to produce a low barometer and a powerful indraught, but quite adequate also to the mitigation of climate there.
865. Influences favourable to heavy precipitation,—Mere altitude, with its consequent refrigeration, does not seem as favourable as mountain peaks and solid surfaces to the condensation and precipitation of vapour in the air. In the trade-wind regions out at sea it seldom rains; but let an island rise never so little above the water, and the precipitation upon it becomes copious. In Colonel Sykes' (§ 299) rain-fall at Cherraponjie, we have an annual precipitation[5] at the rate of 577.6 inches during the six months of S.W. monsoons—from May to October. Surely no one will maintain that this vapour, after rising from the sea, reached the height of 4500 feet for the first time when it was blown upon the peaks of Cherraponjie. Islands in the South Sea are everlastingly cloud-capped. If it be mere refrigeration that condenses this vapour, why, one might ask, should not the clouds form at the same height above the sea whether there be an island below or not, and why should not these clouds precipitate as copiously upon the water, as they do upon the land? "We only know that they do not.
866. The climates of corresponding shores and latitudes north and south.—Captains King and Fitzroy exposed their rain gauge on the western slopes of the Patagonian Andes, and it collected 153.75 inches in forty-one days; that is, at the rate, as already (§ 827) stated, of 1368.7 inches in the year. The latent heat that is liberated during these rains gives to Eastern Patagonia its mild climate. It is this latent heat which causes the irregularity in the barometric curve (§ 858) between the parallels of 50°-55° S. Here the westerly winds prevail; they carry over to the eastern coasts the air that, in passing the mountains, is warmed by this liberated heat; and thus, as I have already (§ 729) endeavoured to show, we have an exception to the rule under which meteorologists ascribe cold and severe climates to the windward or western, soft and mild to the leeward or eastern, shores of extra-tropical oceans. Labrador and the Falkland Islands[6] are in corresponding latitudes north and south. They are both on the windward shore of the Atlantic; they occupy relatively the same position with regard to the wind. Labrador is almost uninhabitable on account of the severity of its climate; but in the Falkland Islands and their neighbouring chores the cattle find pasturage throughout the winter. Th thermometrical difference of climate at these two places, north and south, may be taken as a sort of index to the relative difference between the arctic and antarctic climates of our planet.
867. Thermal difference between arctic and antarctic climates.—Along the eastern base of the Rocky Mountains the isotherms mount up[7] towards the north in consequence of the heavy winter precipitation upon the western slopes of these mountains. The heat which is required to convert the water of the Columbia and other rivers into vapour is set free on the mountain range, and the upper Missouri is by this heat kept open for navigation long after the lower and more southern portion of it is frozen up.
868. The influence of aqueous vapour upon winds and climates.—The average evaporation of water from sea and land is estimated to be from one third to one half as much daily as is contained in the great chain of American lakes. The average precipitation equals the evaporation. The heat that is absorbed and evolved in the process of lifting up and letting down such a body of water has a powerful influence upon climates as well as upon winds; it is the chief source of that motive power which gives to the winds their force, to the storm its violence. Six hundred and twenty pounds of aqueous vapour occupy in the open air the space which it takes one thousand pounds of dry air at the same temperature to fill. Now to appreciate the wind begetting power of this vapour, and its heat, let us imagine the air over an area of considerable extent to be saturated with vapour from the sea, and that from some cause, as in a thunder-storm, this vapour is suddenly, or even rapidly, condensed:—The aerial rarefaction over such an area, and consequently the wind-begetting power within it, would be immense, merely on account of the condensation of this vapour; but if we take into the account the rarefying effect of the heat that is set free during the process of condensation and precipitation, we may cease to marvel either at the force of the wind, or the violence of the rain which marks the hurricane; nor need we wonder at the low range of the barometer or the mildness of temperature in all rainy latitudes.
869. How the temperature of air may he raised by crossing mountains,—In the preceding chapter the circumstances have been considered which favour the idea that most of the unknown surface of the antarctic circle is not only land, but that its coasts are probably highlands; that in its topographical features it presents all the conditions that are required for the rapid condensation of the vapour with which the impinging air from the sea is loaded, and that in the valleys beyond mild climates may be expected. The aqueous vapour which the air carries along is one of the most powerful modifiers of climates. It is to the winds precisely what coals are to the steam-ship at sea—the source of motive power. The condensation of vapour is for one what the consumption of fuel is for the other; only with the winds the same heat may be used over and over again, and for many purposes. By simply sending moist air to the top of snow-capped mountains, condensing its moisture, and bringing it down to the surface again, it is made hot. Though by going up the air be cooled, it is expanded, and receives as sensible heat the latent heat of its vapour; being brought down to the surface again, and compressed by the whole weight of the barometric column, it is hotter than it was before by the amount of heat received from its vapour. That we may form some idea as to the modifying influences upon climate which might arise from this source, let us imagine the air as it impinges upon the antarctic continent to be charged with vapour at the temperature of of 40°. In order to arrive at the place of polar calms, it has to cross a mountain range, we will suppose, the summits of which are pushed high up into the regions of perpetual snow. As this air, with its moisture, rises, it expands, cools, and liberates the latent heat of its vapour, which the air receives in the sensible form. Now suppose the expansion due the height of the mountain-top to be sufficient to lower the temperature of dry air to —50°, but, on account of the latent heat which is liberated from the vapour of the moist air, the temperature of the air that has ascended, instead of falling as it crosses the mountain to —50°, as dry air would do, falls, in consequence of the condensation of its vapour, no lower than —30°. Thus, in the case supposed, heat enough has been set free to raise the temperature of the newly-arrived air 20°. Consequently, when this air, which, at the temperature of 40°, came from the sea loaded with vapour, passes the mountain, it loses vapour, but receives heat; descending into the valleys beyond, it is again compressed by the weight of the barometric column, which, let us assume, is the same in the valley as at the sea level on the other side of the mountain. The temperature of this air now, instead of being 40°, will be 60°. A powerful modifier of climate is the latent heat of vapour in the air.
870. Local variations of climate, how caused.—At one time, as has been shown in Chap. IV., this heat is brought down from the cloud region to scorch the earth; at another time it causes the warm air to ascend, and cooling currents to come down from the upper sky. To this cause Dr. Franklin ascribed the cold summer gusts in America that come from the west. To the effect of this vapour and its heat, with the constant vertical circulation imparted to the atmosphere, we owe those variations of our climates which make any given day of one year to differ from its corresponding day of another. Were it not for those vertical movements, our days would gradually grow cooler from midsummer to midwinter; as the sun recedes in the ecliptic, each day, after he reached a certain degree of south declination, would grow cooler and cooler until his return towards the north again; so that were it not for this vertical circulation the temperature of the day of the month, like the rising and the setting of the sun, or the changes of the moon, might be foretold in a calendar.
871.—Aurora australis.—There is not only reason to suppose that the topographical features and the climates of the antarctic regions differ greatly from the topographical features and climates of the arctic, but there is reason to suppose a difference in other physical aspects also. The aurora points to these. "On the morning of the second of September last," says Capt. B. P. Howes, in his abstract log of the " Southern Cross," lat. 58° S., long. 70° W., "at about half-past one o'clock, the rare phenomenon of the aurora australis manifested itself in a most magnificent manner. Our ship was off Cape Horn in a violent gale, plunging furiously into a heavy sea, flooding her decks, and sometimes burying her whole bows beneath the waves. The heavens were black as death: not a star was to be seen when the brilliant spectacle first appeared. I cannot describe the awful grandeur of the scene; the heavens gradually changed from murky blackness till they became like vivid fire, reflecting a lurid, glowing brilliancy over everything. The ocean appeared like a sea of vermilion lashed into fury by the storm; the waves, dashing furiously over our sides, ever and anon rushed to leeward in crimson torrents. Our whole ship, sails, spars, and all, seemed to partake of the same ruddy hues. They were as if lighted up by some terrible conflagration. Taking all together, the howling, shrieking storm, the noble ship plunging fearlessly beneath the crimson-crested waves, the furious squalls of hail, snow, and sleet driving over the vessel and falling to leeward in ruddy showers, the mysterious balls of electric fire resting on our mast-heads, yard-arms, etc., and above all, the awful sublimity of the heavens, through which coruscations of auroral light would often shoot in spiral streaks and with meteoric brilliancy, altogether presented a scene of terrible grandeur and awful sublimity surpassing the wildest dreams of fancy. Words fail to convey any just idea of the magnificence it presented. One must see it and feel it in order to realize it. I have written this because I believe it an unusual occurrence to see the 'southern lights' at all, and also because this was far superior, and, in fact, altogether different from our northern lights, as seen from the latitude of Boston."
872.—An erroneous opinion.—Some objections to these views respecting the comparative mildness of antarctic climates are suggested by common opinion. It is an opinion which is generally received among sailors and physicists that the southern is colder than the northern hemisphere, and that the austral are more severe than the boreal climates, and that the antarctic icebergs, in the silent evidence afforded by their size and numbers, are witnesses of the fact. These objections have an apparent weight; they deserve consideration.
873.—Tropical regions of the southern hemisphere cooler, extra-tropical warmer, than those of the northern.—The answer to them is as follows : Between lat. 40° or lat. 45° and the equator, and parallel for parallel, the southern hemisphere is cooler than the northern. Reason teaches, and observations show that it is so. But beyond 45° S. observations are wanting, and we are left to reason and conjecture. That the southern hemisphere should, till within a certain distance of the pole, be warmer in winter and cooler in summer, may be explained by the fact that the southern hemisphere has more water; that water being more equable than land in its temperature, produces more equable climates; that the vapour which is taken up from trans-equatorial seas and condensed into rains for cis-equatorial rivers conveys with it a vast amount of heat which the southern hemisphere receives from the sun. It is rendered latent by evaporation on one side of the equator, and made sensible by precipitation on the other. Much of it is set free in the equatorial calm belt, and it is this liberated heat which assists mightily to maintain the thermal equator in its northern position.
874. Formation of southern icebergs,—So, in like manner, the vapour that is borne to the antarctic regions by the polar-bound winds transports immense volumes of heat from the more temperate latitudes of the south, and sets it free again in the polar regions there. And as for the southern icebergs, they are rather of fresh than of salt water; and they are the channels through which the water that the winds carry there as vapour finds its way back again. Being fresh water, and falling on the antarctic declivities of the land, it is by rills, and streams, and rains brought together, and by constant accretions formed into glaciers of a size and thickness that are almost impossible to be formed out of sea water unless it be dashed up as spray. Moreover, on the arctic ocean the rains are not so copious, and for that reason, though the climate be more severe, icebergs, or rather glaciers, are not formed on so grand a scale. Southern icebergs are true glaciers afloat. Arctic winds are dry enough to evaporate much of the ice and snow that fall and form in the north polar basin. As compared with arctic climates, antarctic are marine, arctic continental; and for the very reason that the English climate is cooler in summer and warmer in winter than the Canadian, so is winter at the south pole much less severe than winter at the north. The relative difference between the two polar climates is, as the barometer indicates, even greater than is the difference between a Canadian and an English winter.
875. Mild climate in 63° S.—As tending to confirm these views touching the mildness of unknown antarctic climates, the statement of Captain Smyley, an American sealer, may be mentioned. He planted a self-registering thermometer on the South Shetlands, lat. 63° S., and left it for several winters, during which time it went no lower than—5° Fahr.[8]
876. Antarctic ice-drift.—The low barometer and the implied heavy precipitation in the antarctic regions are not the only witnesses that may be called up in favour of bluffs and bold shores to the antarctic continent. The icebergs, in their mute way, tell that the physical features of that unexplored land are such, in its northern slopes, as to favour the formation of glaciers on the shore, thence to be launched and become the huge icebergs that, on their journey to the milder climates of the north, are encountered far away at sea. After a somewhat attentive, but by no means a thorough, examination and study of antarctic icebergs as they endanger the routes of navigation, the idea suggested itself that information might be gathered from them concerning antarctic regions which would be highly useful to any future expedition thitherward.
877. Antarctic currents.—The conditions required for Gulf-Stream like currents, or a rapid flow and reflow of equatorial and polar waters between the torrid and the frigid zones, as in the northern hemisphere, are not to be found about the antarctic regions. Of all the currents that come from those regions, Humboldt's current is by far the most majestic. It is believed also to be the least sluggish of them all. It certainly conveys the coldest water thence to the torrid zone; and yet it appears not to come from a nursery of icebergs, for in its line of march fewer icebergs are found than are encountered on the same parallels between other meridians, but where feebler currents flow. From the arctic regions the strongest currents bring down the most icebergs; not so from the antarctic. Hence the inference that, though icebergs have been encountered off the shores of the antarctic continent wherever they have been approached, yet it is only those which have been launched from particular points of that frost-bound coast which are stout enough to bear transportation to the parallel of 40° south. In Humboldt's current it is rare to see an iceberg as far from the pole as the parallel of the fifty-fifth degree of south latitude; but off the Cape of Good Hope on one side of the Atlantic, and Cape Corrientes on the other, antarctic icebergs are sometimes seen as far as the parallel of 35°, often as far as 40° Lieutenants Warley and Young, after having examined the logs of 1843 ships cruising on the polar side of 35° S., report the great antarctic ice-drift to be towards the Falkland Islands on one hand, and the Cape of Good Hope on the other.
878. Antarctic explorations demanded.—These facts and the stories of the icebergs are very suggestive. In mute eloquence and with great power they plead the cause of antarctic exploration. Within the periphery of that circle is included an area equal in extent to one-sixth part of the entire land surface of our planet.[9] Most of this immense area is as unknown to the inhabitants of the earth as is the interior of one of Jupiter's satellites. With the appliances of steam to aid us, with the lights of science to guide us, it would be a reproach to the world to permit such a large portion of its surface any longer to remain unexplored. For the last 200 years the Arctic Ocean has been a theatre for exploration; but as for the antarctic, no expedition, has attempted to make any persistent exploration, or even to winter there.
879. Former-expeditions.—England through Cook and Ross; Russia through Billingshausen; France through D'Urville; and the United States through Wilkes, have sent expeditions to the South Sea. They sighted and sailed along the icy barrier, but none of them spent the winter or essayed to travel across and look beyond the first impediment. The expeditions which have been sent to explore unknown seas have contributed largely to the stock of human knowledge, and they have added renown to nations, lustre to diadems. Navies are not all for war. Peace has its conquests, science its glories; and no navy can boast of brighter chaplets than those which have been gathered in the fields of geographical exploration and physical research.
880. An appeal for others.—The great nations of the earth, have all, with more or less spirit, undertaken to investigate certain phenomena touching the sea, and, to make the plan more effectual, they have agreed to observe according to a prescribed formula. The observations thus made have brought to light most of the facts and circumstances which indicate the existence within the antarctic circle of a mild climate mild by comparison. The observations which have led to this conclusion were made by fellow-labourers under all flags. It is hoped that this circumstance may vindicate, in the eyes of all, the propriety of an appeal in this place for antarctic exploration, and plead for it favourable consideration among all nations.
- ↑ Polar winds blow toward the pole, equatorial toward the equator.
- ↑ 2.0 2.1 Maandelijksclie Zeibaanwijzingen van Java naar Het Kanaal. Als Litkomsten Wetenschap en Ervaring Aangaande Winden on Zeestroomingen in Sommige Gedeetten Van Den Oceaan Uitgegenen Door Meet Koninklijk Nederlandsch Meteorologische Institut. Utrecht, 1859.
- ↑ The mean height of the barometer for England generally is 29.94°.—Admiral Fitzroy
- ↑ Captain M'Clintock, during his northern explorations in the schooner "Fox," records the arctic barometer as high as 31 inches.
- ↑ Export of the twenty-second meeting of the British Association for the Advancement of Science, held at Belfast in September, 1852.
- ↑ Maury's Sailing Directions, sixth edition, p. 553.
- ↑ Blodget's Climatology of the United States.
- ↑ Maury's Sailing Directions.
- ↑ The area of the antarctic circle is 8,155,000 square miles.