THERMAL SPRINGS. 185 



earthquake. In this, there prevails a volcanic power, which 

 in its essential nature only acts dynamically, producing 

 movement and commotion, but when it is favoured at parti- 

 cular points by the fulfilment of subsidiary conditions, it is 

 capable of bringing to the surface material products, although 

 not of generating them like true volcanoes. Just as water, 

 vapours, petroleum, mixtures of gases, or pasty masses (mud 

 and moya} are thrown out, through fissures suddenly opened 

 in earthquakes sometimes of short duration, so do liquid and 

 aerial fluids flow permanently from the bosom of the earth 

 through the universally diffused network of communicating 

 fissures. The brief and impetuous eruptive phenomena are 

 here placed beside the great peaceful spring-system of the 

 crust of the earth, which beneficently refreshes and supports 

 organic life. For thousands of years it returns to organized 

 nature the moisture which has been drawn from the atmo- 

 sphere by falling rain. Analogous phenomena are mutually 

 illustrative in the eternal economy of nature ; and wherever 

 an attempt is made at the generalisation of ideas, the inti- 

 mate concatenation of that which is recognized as allied must 

 not remain unnoticed. 



The widely disseminated classification of springs, into 

 cold and hot, which appears so natural in ordinary conversa- 

 tion, has but a very indefinite foundation when reduced 

 to numerical data of temperature. If the temperature of 

 springs be compared with the internal heat of man (found, 

 with thermo-electrical apparatus, to be 98 98. 6 F. according 

 to Brechet and Becquerel), the degree of the thermometer at 

 which a fluid is called cold, warm, or hot, when in contact 

 with parts of the human body, is very different according to 

 individual sensations. No absolute degree of temperature 

 can be established, above which #, spring should be desig- 

 nated warm. The proposition to call a spring cold in any 

 climatic zone, when its average annual temperature does not 

 exceed the average annual temperature of the air in the sama 

 zone, at least presents a scientific exactitude, by affording a 

 comparison of definite numbers. It has the advantage of lead- 

 ing to considerations upon the different origin <?f springs, as 

 the ascertained agreement of their temperature with the 

 annual temperature of the air is recognized directly in un- 

 changeable springs; and in changeable ones, as has beeu 



