liV PROCEEDINGS OF tllE GEOLOGICAL SOCIETY. 



These observations on the temperature of the water are highly 

 curious and important. We have a temperature of 261° of Fahr. at 

 the bottom of a free open column of water, in which thermometers 

 could be suspended on a line dropped from the surface, while it 

 might have been expected that as soon as a film of water at the 

 bottom was raised to a higher temperature, it would ascend, and 

 be replaced by a colder and heavier film, and that thus a constant 

 current would 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 Co- 

 hesion of Liquids, may perhaps be considered as throwing some 

 light on this phsenomenon of the Geyser. By a series of carefully 

 conducted experiments M. Donny has shown : — 



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

 ordinary atmospheric pressure, depends upon its containing a con- 

 siderable 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 tem- 

 perature 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 ordinary- 

 atmospheric pressure, without its exhibiting any symptom of ebul- 

 lition ; showing, that the cohesion of the molecules was nearly equal to 

 the pressure of three atmospheres on water containing air. This is a 

 fact most important to bear in mind in reasoning upon many geolo- 

 gical phaenomena, 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 explo- 

 sion. 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. 



