Note 20 — ON STEPPES AND DESERTS.

p. 8.—“The Southern Hemisphere is cooler and more humid than the Northern.”

Chili, Buenos Ayres, the southern part of Brazil, and Peru, enjoy the cool summers and mild winters of a true insular climate, owing to the narrowness and contraction of the continent towards the south. This advantage of the Southern Hemisphere is manifested as far as 48° or 50° south lat., but beyond that point, and nearer the Antarctic Pole, South America is an inhospitable waste. The different degrees of latitude at which the southern extremities of Australia, including Van Diemen’s Island, of Africa, and America, terminate, give to each of these continents its peculiar character. The Straits of Magellan lie between the parallels of 53° and 54° south lat.; and notwithstanding this, the thermometer falls to 41° Fahr. in the months of December and January, when the sun is eighteen hours above the horizon. Snow falls almost daily in the lowlands, and the maximum of atmospheric heat observed by Churruca in 1788, during the month of December, and consequently in the summer of that region, did not exceed 52°.2 Fahr. The Cabo Pilar, whose turret-like rock is only 1394 feet in height, and which forms the southern extremity of the chain of the Andes, is situated in nearly the same latitude as Berlin.^[EH]

Whilst in the Northern Hemisphere all continents fall, in their prolongation towards the Pole, within a mean limit, which corresponds tolerably accurately with 70°, the southern extremities of America. (in Tierra del Fuego, which is so 108deeply indented by intersecting arms of the sea,) of Australia, and of Africa, are respectively 34°, 46° 30′ and 56° distant from the South Pole. The temperature of the unequal extents of ocean which separate these southern extremities from the icy Pole contributes essentially towards the modification of the climate. The areas of the dry land of the two hemispheres separated by the equator are as 3 to 1. But this deficiency of continental masses in the Southern Hemisphere is greater in the temperate than in the torrid zone, the ratio being in the former at 13 to 1, and in the latter as 5 to 4. This great inequality in the distribution of dry land exerts a perceptible influence on the strength of the ascending atmospheric current, which turns towards the South Pole, and on the temperature of the Southern Hemisphere generally. Some of the noblest forms of tropical vegetation, as for instance tree-ferns, advance south of the equator to the parallels of from 46° to 53°, whilst to the north of the equator they do not occur beyond the tropic of Cancer.^[EI] Tree-ferns thrive admirably well at Hobart Town in Van Diemen’s Land (42° 53′ lat.), with a mean annual temperature of 52°.2 Fahr., and therefore on an isothermal line less by 3°.6 Fahr. than that of Toulon. Rome, which is almost one degree of latitude further from the equator than Hobart Town, has an annual temperature of 59°.7 Fahr.; a winter temperature of 46°.6 Fahr., and a summer temperature of 86° Fahr.; whilst in Hobart Town these three means are respectively 52°, 42°.1, and 63° Fahr. In Dusky Bay, New Zealand, tree-ferns thrive in 46° 8′ lat., and in the Auckland and Campbell Islands in 53° lat.^[EJ]

In the Archipelago of Tierra del Fuego, having a mean winter temperature of 33° Fahr., and a mean summer temperature of only 50° Fahr., in the same latitude as Dublin, Captain King found “vegetation thriving most luxuriantly in large woody-stemmed trees of Fuchsia and Veronica;” whilst this vigorous vegetation, which, especially on the western coast of America (in 38° and 40° south lat.), has been 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 109lichens, Terres de Désolation, as they have been called by French navigators, lie far to the north of the Antarctic Polar Circle; whilst in the Northern Hemisphere, in 70° lat., on the extremest verge of Scandinavia, fir-trees reach a height of more than 60 feet.^[EK] If we compare Tierra del Fuego, and more particularly Port Famine, in the Straits of Magellan, 53° 38′ lat., with Berlin, which is situated one degree nearer the equator, we shall find for Berlin, 47°.3 38°.9 62°.3; and for Port Famine, 42°.6 34°.7 50°.0 Fahr. I subjoin the few certain data of temperature which we at present possess of the temperate zones of the Southern Hemisphere, and which may be compared with the temperatures of northern regions in which the distribution of summer heat and winter cold is so unequal. I make use of the convenient mode of notation already explained in which the number standing before the fraction indicates the mean annual temperature, the numerator the winter, and the denominator the summer temperature.

Places. South Latitude. Mean Annual, Winter, and Summer Temperatures.

54°.5

Sydney and Paramatta (New Holland) 33° 50′ 64°.6

77°.5

58°.5

Cape Town (Africa). 33° 55′ 65°.7

73°.2

52°.5

Buenos Ayres 34° 17′ 62°.4

73°.0

57°.4

Monte Video 34° 54′ 67°

77°.5

42°.1

Hobart Town (Van Diemen’s Land) 42° 45′ 52°.5

63°.0

34°.7

Port Famine (Straits of Magellan) 53° 38′ 42°.6

50°.0