Hot and Thermal Springs. 139 



perature. Unfortunately the extent of this effect is impossible 

 to be determined. 



In Chap. VI. we noticed the natural ice-grottos, and, in ge- 

 neral, all points which possess a temperature lower than the 

 mean temperature at the surface. We then asserted, with great 

 plausibility, that their number might easily be increased with 

 a little attention. Several philosophers, and, among others, 

 Kupffer*, have wished to explain this phenomenon, by suppos- 

 ing that the cold air which sinks into such caverns in the win- 

 ter, cannot, by reason of its greater specific gravity, easily re- 

 ascend during the summer, or, at least, that it only gives way 

 for other colder layers. Although this explanation will not 

 suffice in all cases, yet in many it may be admissible. This 

 granted, the observations on the increase of temperature in the 

 earth would suffer material interruptions in places where cir- 

 cumstances are similar to those necessary for the existence of 

 ice-grottos. The above-mentioned observations in the Erzge- 

 birge, furnished exemplifications of this fact. 



CoAP. XV What injltience has climate on the progression of the 



increase of temperature towards the centre of the Earth ? 



Although circumstances of climate may cause differences of 

 several degrees between the mean temperature of places situat- 

 ed in the same latitude, at the same elevation, and at no great 

 distance apart, yet it cannot well be supposed that the in- 

 fluence of such variations would be felt to any great depth in 

 the earth's crust, indeed it could hardly extend beyond the 

 point where the temperature becomes constant. In such a 

 case the progression of the increase of temperature would be 

 found very different in those places. 



The chmate of a place is influenced by a superabundance of 

 woodland and humidity, and consequently by aridity and 

 barrenness; the former causing cold, and the latter increas- 

 ing the warmth of the climate ; further, by the radiation of 

 heat from heated plateaus, the nature of the soil, the vicinity 

 of glaciers, the accumulation of clouds, and so forth. Thus, 



• Toggeu. Ann. vol. xvi. p. 202, See also Keich. p. 20r 



