502 PHYSICAL GEOGRAPHY. 



temperature indicated was 75'5, while that of the country is 50 ; and consequently the 

 increase of heat there is at the rate of 1 for every 54 feet. 



At Giromagny, in the Vosges, the annual temperature at the surface is 49 ; at 330 

 feet depth it is 53'6 ; at 1008 feet, 65-8 ; at 1416 feet, 74'6. 



In four of the deepest mines of Saxony the annual temperature at the surface is 46'4 ; 

 at from 510 to 600 feet depth, it is 54-5 ; at 840 feet, 58 ; at 1080 feet, 62-6. 



In the deepest British coal mine, that of Killingworth, the annual temperature at the 

 surface is 48 ; at 900 feet depth it is 70 ; at 1200 feet, 77. A similar gradation is 

 found in many of the deeper mines at home and abroad. 



There is thus in the Vosges an increase of temperature in descent below the surface 

 amounting to about 1 in every 60 feet ; in Saxony 1 in every 66 feet ; and in Britain 1 

 in every 45 feet. After the ratio observed in the Vosges, the temperature of the hot springs 

 at Bath, 113, will be found at three-quarters of a mile in the interior of the earth, and that 

 of boiling water at a depth of nearly two miles. " The facts strongly support three conclu 

 sions : First, that the heat of an interior shell of the earth is greater than the superficial 

 shell. Second, that this heat augments progressively as we descend towards this region, in a 

 ratio bearing some relation to the depth. Third, that, even at moderate depths, this heat 

 is greater than the mean heat of the globe ought to be, if entirely derived from the sun. The 

 heat of such an interior mass must be constantly diffusing itself towards the surface ; and 

 at the surface it may be kept down, so as to affect the temperature derived from the solar 

 action very feebly, by the greater or less rapidity of its dissipation. But as it is very 

 improbable that it should be diffused with perfect equality round the whole exterior shell 

 of the globe, it may be the true source of some of those anomalies of climate, such as 

 the discrepancy in the annual heat under the same parallel, which cannot be easily referred 

 to other known causes." If the heat of the globe were entirely derived from the sun, 

 Pekin, at an inconsiderable elevation above the sea, ought to have the same mean annual 

 temperature as Naples, being under the same parallel of latitude ; but instead of this 

 being the case, the temperature falls short of that at Naples by nearly 9. Other causes 

 may contribute to produce this discrepancy ; yet it is not unreasonable to suppose that 

 the mean heat at Naples is raised by its proximity to a focus of internal heat which 

 smokes and flashes through the chimney of Vesuvius. 



No reference has yet been made to physical climate in the southern hemisphere, respect 

 ing which opinion has recently been considerably modified. The idea long prevailed that 

 the whole region south of the equator had a much lower temperature than the northern 

 side ; but it is now sufficiently ascertained, that there is no discrepancy whatever in its 

 equinoctial districts. The Isle of France has the same annual temperature, 80-1, as 

 Jamaica and St. Domingo, under a corresponding northern parallel. The mean tempera 

 ture at Rio Janeiro is 74-5, and at Havannah, at a similar latitude north, it is 76-4. 

 The amount of annual heat about the parallel of 34 of south and north latitude exhibits 

 a remarkable equality, as appears from the following comparison : 



Lat. Mean Temp. 



Southern Hemisphere Sydney, New South Wales - - 33 51' 56-7 



Cape of Good Hope - 33 53 66*9 



City of Buenos Ayres - - 34 36 



Northern Hemisphere Natchez - - 31 28 



Funchal - - 32 37 



Algiers - - - 36 48 



Under the parallel of 51 25' south, the mean temperature of the Falkland Isles is 

 47-3 ; and at the same latitude north we find the mean temperature in Europe from 50 



