THERMAL SPRINGS. 191 



depth of 75 feet. The temperature of the water, which 

 constantly fills the basin, is 180°. At very regular inter- 

 vals of one hour and 20 or 30 minutes the thunder below 

 proclaims the commencement of the eruption. The jets of 

 water, of 9 feet in thickness, of which about three large 

 ones follow one another, attain a height of 100 and some- 

 times 150 feet. The temperature of the water ascending in 

 the funnel has been found to be 260° -G at a depth of 72 

 feet a little while before the eruption, during the eruption 

 255°-5, and immediately after it 251°*6; at the surface of 

 the basin it is only 183° — 185°. The Strokkr, which is also 

 situated at the base of the Bjarnafell, has a smaller mass of 

 water than the Geyser. The sinter margin of its basin is 

 only a few inches in height and breadth. The eruptions 

 are more frequent than in the Geyser, but do not announce 

 themselves by subterranean thunder. In the Strokkr the 

 temperature during the eruption is 235° — 239° at a depth 

 of 42 feet, and almost 212° at the surface. The eruptions 

 of the intermittent boiling springs, and the slight changes in 

 the type of the phenomena, are perfectly independent of the 

 eruptions of Hecla, and were by no means disturbed by the 

 latter in the years 1845 and 1846." With his peculiar 

 acuteness in observation and discussion, Bunsen has refuted 

 the earlier hypotheses regarding the periodicity of the Gey- 

 ser eruptions (subterranean caldrons, which, as steam-boil- 

 ers, are filled sometimes with vapors and sometimes with wa- 

 ter). According to him the eruptions are caused by a por- 

 tion of the column of water, which has acquired a high tem- 

 perature at a lower point under great pressure of accumu- 

 lated vapors, being forced upward, and thus coming under 

 a pressure which does not correspond with its temperature. 



* Sartorius von Waltershausen, Physisch-geographische Skizze von 

 Island, mit besonderer Riicksicht auf Vidkanische Erscheinungen, 1847, 

 s. 128-132 ; Bunsen and Descloiseaux, in the Comptes rendus des Se- 

 ances de VAcad. des Sciences, t. xxiii., 1846, p. 935; Bunsen, in the 

 Annalen der Chemie und Pharmacie, bd. lxii., 3847, s. 27-45. Lottin 

 and Robert had already found that the temperature of the jet of wa- 

 ter in the Geyser diminishes from below upward. Among the forty 

 silicious bubbling springs, which are situated in the vicinity of the 

 Great Geyser and Strokkr, one bears the name of the Little Geyser. 

 Its jet of water only rises 20 or 30 feet. The term boiling springs 

 (Kochbrunnen) is derived from the word Geyser, which is connected 

 with the Icelandic giosa (to boil). On the high land of Thibet also, 

 according to the report of Esoma de Koros, there is, near the Alpi?ie 

 Lake Mapham, a Geyser, which rises to the height of 12 feet. 



