246 68 



vapour can easily be calculated, provided that the height of the barometer and the 

 temperature of the water are known. Hence it follows that, in the case of two 

 springs with the same temperature and at the same pressure of the atmosphere, 

 the spring that evolves the greater volume ot gas in proportion to the volume of 

 water, will lose the greater amount of heal by ebullition. For in this case the 

 evaporation is proportional to the volume of the spring gases. 



As a rule, the spring gas augments the evaporation of the spring water, and 

 thus contributes to keep its temperature below boiling point. The loss of heat 

 consequent on boiling is therefore greater in springs evolving much gas than in 

 springs with slight gas evolution. 



A glance at the temperature of the hot springs investigated, shows that springs 

 in the same locality have practically the same, temperature. In most cases where 

 considerable divergencies from this rule occur, a direct observation of the springs 

 on the spot will show that these divergencies are due to some special peculiarities 

 in regard to the process of cooling. 



Springs in the same locality not only resemble each other as regards their 

 temperature, but in the composition of their spring gases, as Table I shows. The 

 same may be said in regard to the amount of emanation contained in the gas. 



All this seems to indicate that springs in the same locality have a common 

 source, or at least originate under similar conditions. The well-known fact, that 

 the hot springs are always found in fissures in the earth's crust confirms this. At 

 Reykir, (Plate II b), at Grafarbakki, (Plate VII b), and at Reykjafoss, (Plate IX a), it is 

 noticeable that the principal springs are situated almost in a straight line, showing the 

 direction of the fissures. Where the surface of the earth is much disintegrated, as 

 it is around the solfataras, it is not so noticeable that the hot springs are confined 

 to fissures. Every visible sign of the fissures is destroyed by the disintegration of 

 the surface, and the hot springs find their outlets at the lowest places possible. 



Our knowledge of the processes taking place in the depth of the earth, where 

 the real source of the energy of the springs is situated, is very slight, and the 

 available methods of investigation very limited, in that we are almost exclusively 

 confined to the study of the exhalations of the springs, viz. the steam, the spring 

 gases and the radioactive emanations. 



As far as I know, no analyses of spring gases from the places I investigated 

 have been made, except Bunsens' and O. T. Christensen's" analyses of spring 

 gases from the hot springs in the vicinity of Myvatn. I have already pointed out 

 that many hot springs have changed in the course of time. The mention of these 

 changes served particularly to illustrate the action of the hot springs on the outer 

 crust of the earth, and the influence of meteorological conditions and earthquakes 

 on the thermal activity of the springs. 



The matter has another aspect, if one considers the change in the composition 



' Pogg. Ann. 83; p. 238. 1851. 



2 Tidsskrift for Pliysik og Oiemie. 10, p. 225. 1889. 



