SUBTERRANEAN WATERS. 459 



covery of small subterranean collections or currents of water, and 

 some persons have acquired, by a moderate knowledge of tbe 

 superficial structure of the earth combined with long practice, a 

 skill in the selection of favorable places for digging wells which 

 seems to common observers little less than miraculous. The 

 Abbe Paramelle — a French ecclesiastic who devoted himself for 

 some years to this subject and was extensively employed as a 

 well-finder — states, in his work on Fountains, that in the course 

 of thirty-four years he had pointed out more than ten thousand 

 subterranean springs, and though his geological speculations were 

 often erroneous, high scientific authorities have testified to the 

 great practical value of his methods, and to the general accuracy 

 of his predictions.* 



Hydrographical researches have demonstrated the existence of 

 subterranean currents and reservoirs in many regions where 

 superficial geology had not indicated their probable presence. 

 Thus, a much larger proportion of the precipitation in the vaUey 

 of the Tiber suddenly disappears than can be accounted for by 

 evaporation and visible flow into the channel of the river. Cas- 

 telli suspected that the excess was received by underground 

 caverns, and slowly conducted by percolation to the bed of the 

 Tiber. Lombardini — than whom there is no higher authority — 

 concludes that the quantity of water gradually discharged into 

 the river by subterranean conduits, is not less than three-quarters 

 of the total dehvery of its basin.f According to Tucci, Ccmv- 

 jpdgna di Roma, the etiage or extreme low-water delivery of the 

 Tiber does not fall below YO per cent, of its mean delivery for 

 the year. 



What is true of the hydrology of the Tiber is doubtless more 

 or less true of that of other rivers, and the immense value of 

 natural arrangements which diminish the danger of sudden floods 

 by retaining a large proportion of the precipitation, and of an 

 excessive reduction of river currents in the droughts of summer, 

 by slowly conducting into their beds water accumulated and 



* PAKAMELiiE, Qmllenhunde, mit einem Vorwort von B. Cotta, 1856. 



f See LoirBARDiNi, Importama degli studi sulla Statistica dei Fiumi, p. 27 ; 

 also, same author, Sulle Inondazioni avvenute in Franeia, etc., p. 29. 



For an experiment to show the escape of water from the Danube into th« 

 Aach, see Nature, Jan. 17th, 1878, p. 253. 



