180 On the Temperature of the Geyser Springs in Iceland. 



be established throughout the column, until the whole arrived at a 

 temperature of 212°, when ebullition would commence and continue. 

 The pressure of the column of water may perhaps account for the 

 high temperature at the bottom, especially if the free circulation be 

 impeded by the sides of the well not being vertical, and still more by 

 projections in the sides causing contractions of its diameter. But the 

 experiments of M. Donny, of the University of Ghent, published in 

 the 17th volume of the Memoirs of the Royal Academy of Sciences 

 and Belles Lettres of Brussels, on the Cohesion of Liquids, may per- 

 haps be considered as throwing some light on this phasnomenon of 

 the Geyser. By a series of carefully conducted experiments, M. 

 Donny has shewn : — 



1. That the constancy of the boiling point of water, under ordinary 

 atmospheric pressure, depends upon its containing a considerable 

 quantity of air, 



2. That there is a marked difference between the boiling point of 

 water containing air, and of water freed from air. 



3. That a small quantity of air dissolved in water, is sufficient to 

 attenuate greatly the cohesion existing between the molecules of the 

 water. 



4. That when water is freed from air, as far as that is possible, 

 the cohesion of the molecules is so increased, that a higher tempera- 

 ture is necessary to overcome it, and that the boiling point is very 

 considerably raised. 



M. Donny succeeded in raising the temperature of water so freed 

 of air to 135° Centigrade (equal to 275° of Fahr.), under the ordi- 

 nary atmospheric pressure, without its exhibiting any symptom of 

 ebullition, — shewing, that the cohesion of the molecules was nearly 

 equal to the pressure of the three atmospheres on water containing 

 air. This is a fact most important to bear in mind in reasoning 

 upon many geological phsenomena, particularly those connected with 

 the solution of silica. 



The further researches of M. Donny, recorded in the same memoir, 

 appear also to offer an explanation of the violent and intermittent 

 eruptions of the Geyser ; for he states, that if water deprived of air 

 be exposed to so considerable an increase of temperature as to over- 

 come the force of the cohesion of the molecules, the production of 

 vapour is so instantaneous and so considerable as to cause an ex- 

 plosion. As water long boiled becomes more and more deprived of its 

 air, M. Donny attributes the sudden bursting of the boilers of 

 steam-engines to the same cause. — Address delivered at the Anni- 

 versary Meeting of the Geological Society of London, By Leo- 

 nard Horner, 



