182 



COSMOS. 



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 investigations 

 by aerostatic voyages in the free aerial ocean, beyond the 

 near action of the earth, are still very rare, and therefore 

 but little adapted to furnish the numerical data of average 

 conditions which are so necessary. Upon the decrease of 

 heat in the depths of the ocean observations are not want- 

 ing; but currents, which bring in water of different lati- 

 tudes, depths, and densities, prevent the attainment of gen- 

 eral 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 in- 

 fluence of the vertical distribution of heat in the solid crust 

 of the earth, and the system of the geo-isothermic lines, not 

 in too isolated a condition, but as a part of the all-penetrat- 

 ing motion of heat, a truly cosmical activity. 



Instructive as are, in many respects, observations upon 

 the unequal diminution of temperature of springs which do 

 not vary with the seasons as the height of their point of 

 emergence increases still the local law of such a diminish- 

 ing temperature of springs can not be regarded, as is often 

 done, as a universal geothermic law. If we were certain 

 that waters flowed unmixed in a horizontal stratum of great 

 extent, we might certainly suppose that they have gradually 

 acquired the temperature of the solid ground, but in the 

 great net-work of fissures of elevated masses this case can 

 rarely occur. Colder and more elevated waters mix with 

 the lower ones. Our mining operations, inconsiderable as 

 may be the depth to which they attain, are very instructive 

 in this respect ; but we should only obtain a direct knowl* 

 edge of the isogeothermal lines if thermometers were buried, 



