12 FIRESIDE SCIENCE. 



grit Geysers in Iceland, to which allusion has been 

 made, are the most remarkable examples of inter- 

 mittent springs which the- world affords. The 

 smallest of these flows for fifteen or twenty minutes 

 every two hours, and the largest only once in 

 twenty-four or thirty hours. Some interesting pa- 

 pers have been written upon these springs, in which 

 ingenious theories have been advanced to account 

 for the phenomena* presented. The most reasona- 

 ble explanation is that vapor or steam holds back 

 the column of water at intervals in the same way 

 as does the gas in other springs, and that it is only 

 when this steam pressure is forced to 'give way that 

 the water flows, and thus the periodic accumulation 

 of steam in the pipes causes intermittent flow. 



The term mineral or medicinal has been given 

 to a class of springs, the waters of which hold in 

 solution considerable quantities of mineral salts or 

 agents which are used medicinally. From the most 

 remote ages invalids have resorted to mineral 

 springs with the view of being relieved of certain 

 maladies, and in this country and other parts of the 

 world there are springs which have acquired a rep- 

 utation for extraordinary curative properties. The 

 arrangement of mineral springs at Saratoga is cer- 

 tainly wonderful, and we cannot recur to a group 

 in any part of the world which will at all compare 

 with these, in potency of medicinal character, or 



