38 COSMOS. 



waters acquire the temperature of the terrestrial strata with 

 which they are brought in contact, the water that is ob- 

 tained through borings may, in certain cases, when communi- 

 cating with vertically descending fissures, obtain some aug- 

 mentation of heat from an inaccessible depth. An influence 

 of this kind, which is very different from that of the varying 

 conductive power of different rocks, may occur at individual 

 points widely distant from the original boring. It is pro- 

 bable that the waters in the interior of our earth move in 

 some cases within limited spaces, flowing either in streams 

 through fissures (on which account it is not unusual to find 

 that a few only of a large number of contiguous borings prove 

 successful), or else follow a horizontal direction, and thus form 

 extensive basins a relation which greatly favours the labour 

 of boring, and in some rare cases betrays, by the presence of 

 eels, mussels, or vegetable remains, a connection with the 

 earth's surface. Although from the causes which we have 

 already indicated, the ascending springs are sometimes 

 warmer than the slight depth of the boring would lead 

 us to anticipate, the afflux of colder water which flows 

 laterally through transverse fissures leads to an opposite 

 result. 



It has already been observed that points situated on the 

 same vertical line at an inconsiderable depth within the 

 interior of our earth, experience at very different times 

 the maximum and minimum of atmospheric temperature, 

 which is modified by the sun's place, and by the seasons of 

 the year. According to the very accurate observations of 

 Quetelet, daily variations of temperature are not percep- 

 tible at depths of 3fths feet below the surface ; 37 and at 

 "Brussels, the highest temperature was not indicated until 

 Jie 10th of December in a thermometer which had been 

 Hunk to a depth of more than 25 feet, whilst the lowest tem- 

 perature was observed on the 15th of June. In like manner, 

 in the admirable experiments made by Professor Forbes, in 

 the neighbourhood of Edinburgh, on the conductive power of 

 different rocks, the maximum of heat was not observed until 

 the 8th of January in the basaltic trap of Calton Hill at 

 a depth of 24 feet below the surface. 38 It would appear 



# Quetelet, in the Bulletin de I'Acad. de Bruxelles, 1836, p. 75. 



38 Forbes, Exper. on the temperature of the earth at different depth* 



