THERMAL SPRINGS. 189 



mountain springs burst forth upon vast elevated plateaux, 

 eight or ten thousand feet above the sea (Micuipampa, 

 Quito, Bogota), or in narrow, isolated mountain-peaks many 

 thousand feet higher, not only include a far greater part of 

 the surface of the earth, but also lead to the consideration 

 of analogous thermic conditions in the mountainous countries 

 of the temperate zones. 



In this important subject it is above all things necessary 

 to separate the cycle of actual observations from the theor- 

 etical conclusions which are founded upon them. What we 

 seek, expressed in the most general way, is of a triple nature : 

 the distribution of heat in the crust of the earth which is 

 accessible to us, in the aqueous covering (the ocean) and in 

 the atmosphere. In the two envelopes of the body of the 

 earth, the liquid and gaseous, an opposite alteration of tem- 

 perature (diminution and increase in the superposed strata) 

 prevails in a vertical direction. In the solid parts of the 

 body of the earth the temperature increases with the depth ; 

 the alteration is in the same direction, although in a very 

 different proportion, as in the aerial ocean, the shallows and 

 rocks of which are formed by the elevated plateaux and mul- 

 tiform mountain peaks. We are most exactly acquainted 

 by direct experiments, with the distribution of heat in the 

 atmosphere, geographically by local determination in lati- 

 tude and longitude, and in accordance with hypsometric re- 

 lations in proportion to the vertical elevation above the sur- 

 face of the sea, but in both cases almost exclusively in 

 close contact with the solid and fluid parts of the surface of 

 our planet. Scientific and systematically arranged investi- 

 gations by aerostatic voyages in the free aerial ocean, beyond 

 the near action of the earth, are still very rare, and there- 

 fore but little adapted to furnish the numerical data of 

 average conditions which are so necessary. Upon the de- 

 crease of heat in the depths of the ocean observations are 

 not wanting ; but currents, which bring in water of different 

 latitudes, depths, and densities, prevent the attainment of 

 general results, almost to a greater extent than currents in 

 the atmosphere. We have here touched preliminarily upon 

 the thermic conditions of the envelopes of our planet, which 

 will be treated of in detail hereafter, in order to consider the 

 influence of the vertical distribution of heat in the solid 



