THE ATxMOSPHERE— CLIMATE. 



99 



Bponding season in Montpellier and Flor- 

 ence("3). The relations now indicated show 

 how important for vegetation, agriculture, the 

 growth of fruit, and the feeling of climatic com- 

 fort is the distribution of the same annual mean 

 temperature over the different seasons of the 

 year.* 



The lines which I have entitled isochimenal 

 and isotheral (lines of like mean winter and 

 summer heat) are by no means parallel with 

 the isothermal lines (lines of like mean annual 

 heat). If in places where the Myrtle grows 

 untended, and the ground in winter is never 

 permanently covered with snow, the tempera- 

 ture of the summer and autumn is still just suf- 

 ficient — nay, it might be said, is barely suffi- 

 cient to bring the apple to perfect ripeness ; if 

 the vine, when it yields drinkable wine, flies 

 islands, and almost all sea-boards, even those 

 with a western exposure ; the cause of this 

 does not alone reside in the lower summer 

 temperature of the coasts, which our thermom- 

 eter in the shade proclaims ; it lies in the hith- 

 erto so little considered, and yet in other phe- 

 nomena (such as an explosion of a mixture of 

 chlorine and hydrogen gas) so important dis- 

 tinction between direct and diffused light with 

 a clear or clouded state of the heavens. It is 

 long since I directed the attention of the ob- 

 servers of natural phenomena and of botanical 

 physiologists to these distinctions, as well as 

 to the unestimated heat locally developed in 

 the vegetable cell under the influence of direct 

 light(36*). 



If we descend in the thermal scale of hus- 

 bandry of different kinds(^^^), beginning with 

 the hottest climates, where Vanilla, Cacao, the 

 Banana, Plantain, and Cocoanut Palm are suc- 

 cessfully cultivated, to the regions in succes- 

 sion of the Pine-apple, Sugar-cane, Coffee, 

 Date, Cotton-tree, Citron, Olive, true Chestnut, 

 and Vine yielding drinkable wine, the careful 

 geographical consideration of the limits of each 

 of these species of culture, respect being had 

 at once to the plain and to the mountain slope, 

 assures us that other climatic relations than 

 those connected with the mean annual temper- 

 ature here come into play. To take the single 

 instance, of the vine, I remind my reader, that 

 in order to have palatable wine('**), not only 

 must the mean annual temperature exceed 9^° 

 C. [49°-55 F.], but that the mean winter cold 

 must not fall quite to the freezing point (0°-5 

 C, 33°-4 F.), and this must be followed by a 

 mean summer heat of at least 18° C. [64°-4 F.]. 

 At Bordeaux, in the valley of the Garonne 

 (North latitude 44° 50'), the temperature of the 

 year, of the. winter, of the summer, and of the 

 autumn, are respectively 13°-8; 6°-2 ; 21°-7; 

 and 14°-4. In the plains of the Baltic, where 

 wine is grown that is not palatable, though it 

 is nevertheless consumed, the corresponding 

 numbers are 8°-6 ; —°7; 17°-6; and 8°-6. If 

 it seem strange that the great differences which 

 the cultivation of the vine, favoured or opposed 

 by climate, exhibits, are not more conspicuous- 

 ly shown by our thermumetrical numbers, this 

 strangeness will be lessened by the considera- 



C* For a great deal of interesting informatioa on temper- 

 »ture the reader is referred to an excellent " Thermomet- 

 rical Table," by Alfred S. Taylor, published by Willatt, 98 

 Cheapside. It is a complete Encyclopedia of Thermotics. 

 — Tr.] 



tion, that a thermometer set for observation in 

 the shade, and as effectually as possible pro- 

 tected from the effects of direct insolation and 

 nocturnal radiation, does not by any means 

 give the true superficial temperature for every 

 division of the year, under periodical variations 

 of the heat of the ground, exposed to the whole 

 amount of insolation [and of radiation]. 



In the same way as the milder, more equa- 

 ble climate of the peninsula of Brittany stands 

 related to the climate of the rest of the com- 

 pact continent of France, colder in winter, hot- 

 ter in summer, so to a certain extent does the 

 climate of Europe stand related to that of the 

 general continent of Asia, to which Europe 

 forms, in fact, a kind of western peninsula. 

 Europe owes its milder climate : to the geo- 

 graphical position of Africa, which in its vast 

 extent, favouring the ascending current of air, 

 presents a solid radiating surface within the 

 tropics, whilst southward from Asia the equa- 

 torial region is mostly oceanic ; to its parti- 

 tions and vicinity to the sea — its forming the 

 western boundary of the northern part of the 

 Old World ; to the existence of a sea free from 

 ice, where it extends towards the north. Eu- 

 rope from this would become colder were Af- 

 rica to be overflowed by the sea and to disap- 

 pear(^^^) ; were the Mythical Atlantis to arise 

 and connect Europe with North America ; 

 were the gulf-stream to cease from flowing 

 and pouring its tepid current into the northern 

 sea, or were another continent, raised by vol- 

 canic forces, to intervene between the Scandi- 

 navian peninsula and Spitzbergen. If we see 

 the mean annual temperature of Europe sink- 

 ing as we proceed along the same parallel of 

 latitude from the shores of the Atlantic, from 

 France, through Germany, Poland, and Russia, 

 towards the Ural Mountains, from west to east, 

 therefore, the principal cause of the phenome- 

 non is to be sought for in the progressively less 

 and less subdivided or more compact form of 

 the land as the longitude increases, in the in- 

 creasing remoteness of the tempering ocean, 

 as in the feebler influence of the west wind. 

 Beyond the Ural chain the west becomes the 

 chilling land-wind, for then it is blowing over 

 extensive tracts of country covered with ice 

 and snow. The intense cold of Western Sibe- 

 ria is greatly connected with such relations of 

 configuration in the land and of currents of 

 air(^^'*), nowise, as Hippocrates and Trogus 

 Pompeius presumed, and as distinguished trav- 

 ellers in the 18th century have gone on fancy- 

 ing, with great elevation of the country above 

 the level of the sea. 



If we pass on from the consideration of di- 

 versities of temperature in the plains, to ine- 

 qualities in the polyhedral configuration of the 

 surface of our planet, we contemplate the 

 mountains either according to their influence 

 on the climate of the neighbouring low lands, 

 or according to the influences which they ex- 

 ert, in consequence of hypsometrical relations, 

 upon their own summits, frequently spread out 

 into lofty plateaus or table-lands. The group- 

 ing of mountains into chains divides the sur- 

 face of the earth into diflferent basins, some- 

 times into narrow circular valleys surrounded 

 by lofty walls— circus-like cauldrons, which (as 

 in Greece and a portion of Asia Minor) give in- 



