Note 20 — STEPPES AND DESERTS.

p. 10.—“The Southern Hemisphere is cooler and moister than our Northern half of the globe.”

Chili, Buenos Ayres, and the southern parts of Brazil and Peru, have all, as a result of the narrowness of the continent of South America as it tapers towards the south, a true “insular climate;” or a climate of cool summers and mild winters. As far as the 48th or 50th parallel of latitude this character of the Southern Hemisphere may be regarded as an advantage, but farther on towards the Antarctic Pole, South America gradually becomes an inhospitable wilderness. The difference of latitude of the southern terminating points of Australia, (including Van Diemen Island), of Africa, and of America,—gives to each of these continents a peculiar character. The Straits of Magellan are between the 53d and 54th degrees of latitude, and yet in December and January, when the sun is 18 hours above the horizon, the temperature sinks to 4° Reaumur, or 41° Fahrenheit. Snow falls almost daily, and the highest atmospheric temperature observed by Churruca (1788) in December, (the summer of those regions), was not above 9° R., or 52°.2 Fahr. The Cabo Pilar, whose towering rock, though only 218 toises, or 1394 English feet high, may be regarded as the southern termination of the chain of the Andes, is almost in the same latitude as Berlin. (Relacion del Viage al Estrecho de Magallanes, apendice, 1793, p. 76.)

While in the Northern Hemisphere all the continents attain a sort of mean limit towards the Pole, coinciding pretty regularly with the parallel of 70° the terminating points in the Southern Hemisphere,—of America, in the deeply indented and intersected Tierra del Fuego,—of Australia,—and of Africa,—are respectively 34°, 46½°, and 56° distant from the south pole. The temperature of the very unequal extents of ocean, which divide these southern points from the icy pole, contributes very materially to modify their climates. The areas of dry land in the Northern and Southern Hemispheres are to each other in the proportion of 3 to 1. But this inferiority in extent of continental masses in the Southern Hemisphere, as compared with the Northern, belongs much more to the temperate than to the torrid zone. In the temperate zones of the Northern and Southern Hemispheres, the ratio is as 13 to 1; in the torrid zones as 5 to 4. The great inequality in the distribution of the dry land exercises a very sensible influence on the strength of the ascending aerial current which turns towards the southern pole, and on the temperature of the Southern Hemisphere. Some of the noblest forms of tropical vegetation, for example the tree-ferns, advance south of the equator as far as the parallels of 46°, and of even 53°; whereas north of the equator they are not found beyond the tropic of Cancer. (Robert Brown, Appendix to Flinders’ Voyage, p. 575 and 584; Humboldt, de distributione geographica Plantarum, p. 81–85.) Tree-ferns thrive extremely well at Hobart Town in Van Diemen Island, (lat. 42° 53′), where the mean annual temperature is 9° Reaumur, or 52°.2 Fahrenheit, and is therefore 1°.6 Reaumur, or 3°.6 Fahrenheit, less than that of Toulon. Rome is almost a degree of latitude farther from the equator than Hobart Town, and has an annual temperature of 12°.3 R., or 59°.8 Fahr.;—a winter temperature of 6°.5 R., or 46°.4 Fahr.,—and a summer temperature of 24° R., or 86° Fahr.; these three values being in Hobart Town 8°.9, 4°.5, and 13°.8 R., or 52°.0, 42°.2, and 63°.0 Fahr. In Dusky Bay, New Zealand, tree-ferns grow in S. lat. 46° 8′, and in the Auckland and Campbell Islands, even in 53° S. lat. (Jos. Hooker, Flora Antarctica, 1844, p. 107.)

In the Archipelago of Tierra del Fuego,—where, in the same latitude as Dublin, the mean winter temperature is 0°.4 Reaumur, (33° Fah.) and the mean summer temperature only 8° R., or 50° Fahr.,—Captain King found the “vegetation thriving most luxuriantly in large woody-stemmed trees of Fuchsia and Veronica”; while this vigour of vegetation, which, especially on the western coast of America in 38° and 40° of south latitude, is so picturesquely described by Charles Darwin, suddenly disappears south of Cape Horn, on the rocks of the Southern Orkney and Shetland Islands, and of the Sandwich Archipelago. These Islands, but scantily covered with grass, moss, and lichens, “Terres de Désolation,” as the French navigators call them, are still far north of the Antarctic Circle; whereas in the Northern Hemisphere in 70° of latitude, at the extremity of Scandinavia, fir-trees attain a height of between 60 and 70 English feet. (Compare Darwin in the “Journal of Researches,” 1845, p. 244, with King in vol. i. of the Narrative of the Voyages of the Adventure and Beagle, p. 577.) If we compare Tierra del Fuego, and particularly Port Famine in the Straits of Magellan in lat. 53° 38′, with Berlin, which is one degree nearer the equator, we find for

Berlin 6°.8, -0°.5 R., 47°.2, 30°.8 Fahr.; and for

13°.9 63°.2

Port Famine 4°.7, 1°.2 R., 42°.6, 34°.8 Fahr.

8°.0 50°.0

I subjoin in one view the few well-assured temperature data which we at present possess, for the lands of the temperate zone in the Southern Hemisphere, and which may be compared with the temperatures of the Northern Hemisphere, in most parts of which the distribution into summer heat and winter cold is so different and so much less equable. I employ the convenient method of notation before used and explained in pages 129–131.

Place. South Latitude. Mean Annual, Winter, and Summer Temperature.

Reaumur. Fahrenheit.

Sidney and Paramatta (New Holland.) 33°.50′ 14°.5 10°.0 64°.5 54°.5

—— ——

20°.2 77°.5

Cape Town (Africa.) 33°.55′ 15°.0 11°.8 65°.7 58°.5

—— ——

18°.3 73°.3

Buenos Ayres 34°.17′ 13°.5 9°.1 62°.4 52°.5

—— ——

18°.2 73°.0

Monte Video 34°.54′ 15°.5 11°.3 66°.8 57°.3

——? ——

20°.2 77°.5

Hobart Town (Van Diemen Island.) 42°.45′ 9°.1 4°.5 52°.5 42°.2

—— ——

13°.8 63°.0

Port Famine (Straits of Magellan.) 53°.38′ 4°.7 1°.2 42°.6 34°.8

—— ——

8°.0 50°.0