87 



Now it is evident that in the case of Avater springs that liave a 

 moderate heat and are constant, that the usual effect of hydros- 

 tatic pressure might cause water first to descend and afterwards 

 come to the surface hot, by the short cut of a fault ; but in the 

 case of hot springs that are intermittent, or only the accompani- 

 ments of volcanoes, this could not be the case. For if the water 

 descends by its usual laws, it will only ascend again on the 

 prmciple of finding its own level, which it will do whether it has 

 been heated in its descent or not ; the heating will neither retard 

 nor accelerate its ascent ; if it were otherwise, it would follow that 

 the force of water descending generates force, or in other words, 

 that a certain height of water can at one time give a pressure 

 greater, at another time less. For if the heat were the cause of 

 the Avater rising to the surface, it would at the same time prevent 

 the supply (which only descends by its own Aveight) from coming 

 doAvn, it Avould be forced back. Therefore if a sjjring be inter- 

 mittent, the heat has arisen or accumulated after the Avater has 

 reached a low leA'el, the heat is also intermittent. A spring may 

 be intermittent Avitli the heat permanent under such circum- 

 stances as exist at the great Geyser of Iceland, Avhere the supply 

 seems to percolate into a deep hole, the sides of Av^hich are highly 

 heated. The effect of this is, that as the Avater flows in, it is 

 heated to boiling point, and the water continues just at the 

 boiling point until this fissure or hole is filled to the surfixce, and 

 runs over ; it then appears that from the Avant of heat conducting 

 poAver in Avater, the loAver part of the column is sui^er-heated, and 

 causes those intermittent explosions and the grand fountains of 

 hot Avater that are there. The same effect may be produced on a 

 small scale, by boiling AA'ater in a long narroAV tube in a vertical 

 position. This is peculiar and exceptional, depending on the 

 Avater's loss of aii*. 



Therefore if Avater only rises to the surface by hydrostatic 

 pressure, which is, I think, proved, and that it rises in a boiling 

 state, and if the source of its heat is central, and only increases 



