208 M. Arago 07i Artesian Wells 



level of the Black Sea, is nevertheless not inundated ; nor is it 

 even a marsh, as it ought to be, if the sea, by a continued 

 infiltration, penetrated indefinitely towards the bowels of the 

 earth 



To this theory, whose frail foundation we have been exhibit- 

 ing, another element has been conjoined, viz. a central heat, 

 which is brought to bear not so much on deep wells, as on those 

 fountains which occur at more or less considerable elevations 

 above the level of the sea. With its help, it was the interior 

 vapours, which, either alone or mixed with air, by constant 

 condensation towards the surface, produced there an increas- 

 ing humidity. Such were, in reality, the opinions held by 

 Aristotle, Seneca and Cardan ; we may also add, by Des- 

 cartes, as expressed in his own words, which we quote : " Wa- 

 ter penetrates by many subterranean conduits beneath the moun- 

 tains, whence the internal heat elevates it, in vapour, towards 

 their summits, and there supplies the springs of fountains and of 

 rivers." This conception, in which the globe becomes a kind of 

 alembic, and its exterior crust a sponge, and which has so often 

 been put forward since the time of Descartes, of course to the 

 exclusion of the very simple idea which would lead us to attri- 

 bute the origin of springs to rain-water, is so complicated, as to 

 lead to the inference, that it owes its existence to the necessity 

 experienced in the explanation of some inaccurate ill-understood 

 observation. And such, in fact, was its origin ; or, at all events, 

 it was this circumstance that led it to be regarded with the con- 

 sideration it has received. 



Seneca mentions, in his Questions on natural history, that 

 rain, however abundant it may be, never penetrates into the soil 

 above ten feet : he states that hf is certain nt this, from having 

 made many careful experiments with this object in view. It be- 

 comes a question whether we must not have recourse to internal 

 vapours, in explaining the existence of fountains which are si- 

 tuated far above the level of the sea, whilst their source is also 

 deep under a vast extent of soil. According to the experiments 

 of the o-reater number of naturalists, who have recently engaged 

 in these researches, the permeability of the earth would* be de- 

 cidedly inferior to the limit assigned by Seneca. Thus Ma- 

 riotte maintains, that, in cuUivated lands, the heaviest rains of 



