274 



TIERRA DEL FUEGO. 



June, 1834. 



There are no direct observations, by which to judge of 

 the mean temperature of the year in these southern islands. 

 But after reading the above accounts, it will readily be granted 

 that it must be very low. Even in Georgia, in lat. 54°-55^, 

 it is not improbable that the soil is perpetually frozen 

 at a few feet beneath the surface. At Deception Island in 

 lat. 62°-63° from the preservation of the dead body alluded 

 to, and the interstratification of ice with the volcanic ashes, 

 we may feel almost sure that such must be the case. In the 

 northern hemisphere, it is only on the great continents that 

 so low a mean temperature is found in corresponding lati- 

 tudes. In North America, according to Richardson,^ north 

 of lat. 56°, the thaw does not penetrate to a greater depth 

 than three feet. In the Steppes of Siberia, Humboldt t 

 states that to the northward of 62°, the ground between 

 twelve and fifteen feet below the surface is always frozen. 

 In the space, however, between these t\^ o great northern con- 

 tinents, the line of perpetual congelation rises considerably 

 towards the north. 



It is a remarkable meteorological fact, that in the 

 northern and southern hemispheres, a low mean tempera- 

 ture, in latitudes without the frigid zone, is the result of a 

 directly opposite condition of things. In the northern hemi- 

 sphere the atmosphere is rendered extremely cold, from the 

 radiation of a large extent of country during a long winter ; nor 

 is it moderated by the warmer currents of any neighbouring 

 sea: hence the extreme cold of the winter more than 

 counterbalances the heat of summer. In the southern 

 hemisphere, on the other hand, although the winter is 

 moderate, the summer is cold ; for a sky constantly clouded 

 rarely permits the rays of the sun to warm the surface (itself 

 a bad absorbent) of the great ocean : hence, the mean 

 temperature of the year falls below the freezing point. It 

 will at once be evident, that a kind of vegetation which 

 requires an equable temperature, will approach much nearer 



* Appendix to Back's Expedition, 

 f Fragmens Asiatiques, vol. ii., p. 386. 



