50 Prof. Bischof on the Natural Htsiory of 



lava-channels, or other fissures more recently opened.* But if 

 at that depth, the hydrostatic pressure be greater than the elas- 

 tic force, which the water has there acquired, no steam will he 

 generated in the whole course of the spring ; but, in the con- 

 trary case, from the lowest point up to the point where the elas- 

 tic force becomes greater than the hydrostatic pressure, the wa- 

 ter will escape in the form of a vapour. However high the 

 temperature of the water may be at the lowest point of its course, 

 ■whether in the liquid or in the gaseous state, yet, when it 

 reaches the surface, it cannot exceed the boiling point. Tlic 

 reason of springs but seldom attaining even this maximum may 

 be either the loss of heat communicated to the superior strata of 

 the earth, or that they meet with streams of gas, (carbonic acid, 

 or sulphureted hydrogen), which, even if possessed of a very 

 high temperature, will cause a depression of their temperature, as 

 is proved by experiments cited in Chap. II. of Memoir on Springs, 

 p. S36, vol. XX. Ed. Phil. Journ.t The production of hot 

 springs, according to the last species of volcanic action, may, 

 however, be thus imagined; that the water which descends to 

 the volcanic focus is there converted into steam, which, rising 

 through fissures into higher regions, meets with atmospheric wa- 

 ters which it warms, and wifth them returns to the surface.J 

 The course of hot springs produced in this manner can, there- 

 fore, occur only at inconsiderable depths below the surface. 

 Lastly, it may happen that the lava last raised did not escape 

 from the crater or its lateral openings, but became soHd on it< 



* Von Humboldt is also of opinion, Reise, &c. t. i. p. 187 and 188, that 

 the vapour which rises from the " Narices del Pico" as they are called, and 

 from the rents in the crater of Teneriffe, is nothing but atmospherical water 

 which has penetrated by infiltration. 



+ According to M. Arago, the hottest spring in Europe unconnected witli 

 modern volcanic action is tliat of Chaudesaigues in Awcergne, whose temperii- 

 ture he quotes at 176° Fahr. Annuaire du Bureau des Longitudes, 18 3u. 

 The next hottest to this seems to be 2'huez, in the Pyrenees, whose tempera- 

 ture is, according to Professor Forbes, 171.°5 Fahr. Phil. Trans, t. ii. p. 603, 

 for 182C. Forbes believes, p. 61 0, the baths of Nero, near Naples, the hottest 

 spring on the Continent of Europe, which is connected with modem volca- 

 jiic action, the temperature being 182.°2 Fahr. 



:}: Perhaps the numerous hot mineral springs which rise at the foot of the 

 still smoking mass of rocks on Pantellaria, as well as the numerous hot sid- 

 phureous springs in the vicinity of Sciacca, in Sicili/, have a similar origin. 

 Jloffman, 1. c. 



