THE MECHANICS OF INTERMITTENT SPRINGS. 371 



earth, as, for example, at Yakutsk, in Siberia, where the year's tem- 

 perature does not exceed 13, it need be only a little above that. The 

 waters of thermal springs maintain an equable temperature, and must 

 therefore come out of depths in the earth at which the variations in 

 the temperature of the air exert no influence. According to Boussin- 

 gault, this depth in the tropics is only a little more than one or two 

 feet, but between 48 and 52 of north latitude it is between sixty-six 

 and ninety-three feet below the surface. Besides the springs that are 

 called thermal, many springs are found the temperature of which ex- 

 ceeds the highest mean temperature of the year, and are called warm 

 springs. Examples are the spring at Carlsbad, 167 ; that of Wies- 

 baden, 158 ; those of Baden-Baden, 154 to 111, etc. The depth 

 from which the waters come may be approximately calculated by the 

 rule that the temperature increases one degree for every ninety feet 

 below the surface. Hence the water of the bubbling spring at Carls- 

 bad is supposed to come from a depth of seven thousand three hun- 

 dred feet. 



A third class of springs, the boiling springs, geysers, or hot springs, 

 whose temperature is near the boiling-point of water, are peculiar in 

 respect to the places where they appear. They are found only in vol- 

 canic regions ; are numerous in Iceland, where there are more than a 

 hundred of them ; on the North Island of New Zealand, where they 

 are most abundant in the neighborhood of the Roto Mahana, or Hot 

 Lake ; and near the Yellowstone Lake, the Fire-hole and the Madison 

 Rivers, in the region of the Wind River Mountains, in the United 

 States, where some eight hundred of them are grouped within a cer- 

 tain well-defined area. 



Among the hot springs, those which are intermittent, or the flow 

 of which is uneven, are regarded with particular interest. Their waters 

 are of a crystal clearness, with a slight tinge of green, and contain in 

 solution considerable quantities of silicic acid, which frequently is de- 

 posited, in consequence of the evaporation of the water or the lowering 

 of its temperature, as sinter. The most thorough investigations of the 

 phenomena of intermittent springs have been made at the great 

 geyser at the foot of the Bjarnaf ell in Iceland. Sartorius von Walters- 

 hausen,* Descloiseaux, f and Bunsen, J have made extensive observa- 

 tions upon them, from the results of which, and of their own observa- 

 tions, Mackenzie, Bunsen, and, more recently, O. Lang, have formed 

 theories respecting the mechanical causes of the intermittent flow. 



The-Great Geyser is situated at a height of one hundred and ten 

 metres (three hundred and fifty-seven feet) above the sea. The part 

 accessible to observation consists of a straight cylinder, R, lined with 

 siliceous sinter, S, Fig. 1, about three metres (or ten feet) in diameter, 



* " Physisch-geographische Skizze von Island," 1847. 



f " Competes Rendus," tome xxiii, 1846. 



% " Annalen der Chemie und Pharmacie," Bd. kii. 



