38 COSMOS. 



as of volcanic igneous currents, emanated from the early and 

 generally felt requirement of discovering some common cause 

 for a great and complicated series of phenomena. 



Amid the multiplicity of relations presented by the earth's 

 surface, in respect to insolation (solar action) and its capacity 

 of radiating heat, and amid the great differences in the ca- 

 pacity for conducting heat, which varies in accordance with 

 the composition and density of heterogeneous rocks, it is 

 worthy of notice, that wherever the observations have been 

 conducted with care, and under favorable circumstances, the 

 increase of the temperature with the depth has been found 

 to present for the most part very closely coinciding results, 

 even at very different localities. For very great depths we 

 obtain the most certain results from Artesian wells, especial- 

 ly when they are filled with fluids that have been rendered 

 turbid by the admixture of clay, and are therefore less favor- 

 able to the passage of internal currents, and when they do 

 not receive many lateral affluents flowing into them at differ- 

 ent elevations through transverse fissures. On account of 

 their depth, we will begin with two of the most remarkable 

 Artesian wells, namely, that of Grenelle, near Paris, and 

 that of the New Salt-works at Oeynhausen, near Minden. 

 We will proceed in the following paragraph to give some 

 of the most accurate results which they have yielded. 



According to the ingenious measurements of Walferdin,* 

 to whom we are indebted for a complete series of veiy deli- 

 cate apparatus for determinations of temperature at great 

 depths in the sea and in springs, the surface of the basin of 

 the well at Grenelle lies at an elevation of 36*24 metres, or 

 119 feet, above the level of the sea. The upper outlet of 

 the ascending spring is 33-33 metres, or 109-3 feet, higher. 

 This total elevation of the ascending water (69-57 metres, or 

 228-2 feet) is, when compared with the level of the sea, about 

 196-8 feet lower than the outbreak of the green sandstone 

 strata in the hills near Lusigny, southeast of Paris, to whose 

 infiltrations the rise of the waters in the Artesian wells at 

 Grenelle have been ascribed. The borings extend to a depth 

 of 547 metres, or 1794-6 feet, below the base of the Grenelle 

 basin, or about 510-76 metres, or 1675 feet, below the level 



* The observations of Walferdin were made in the autumn of 1847, 

 and deviate very slightly from the results obtained with the same ap- 

 paratus by Arago, in 1840, at a depth of 1657 feet, when the borer 

 had left the chalk and was beginning to penetrate through the gault. 

 See Cosmos, vol. i., p. 174, and Cornptes rendus, t. xi., 1840, p. 707. 



