XVI NOTES. 



earthy strata through the agency of water, or a precipitation of earth from 

 water. (Middend. S. 167.) 



( 47 ) p. 45. Middendorff, Bd. i. S. 160, 164 and 179. In these numerical 

 estimates and conjectures as to the thickness of the ground ice, an increase of 

 temperature in arithmetical progression with the depth is assumed. Whether, at 

 greater depths, the rate of increase of temperature may become slower, is theo- 

 retically uncertain ; and it is, therefore, not advisable to enter into calculations 

 respecting the temperature at the centre of the Earth in current-exciting molten 

 masses of various kinds. 



(*) p. 46. Schrenk's Eeise durch die Tundern der Samojeden, 1848, Th. i. 

 S. 597. 



C 49 ) p. 46. Gustav. Rose, Reise nach dem Ural, Bd. i. S. 428. 



(**) p. 47. Compare G. von Helmersen's experiments on the relative con- 

 ducting power of different rocks (Me'm. de 1'Acad^mie de St. Pdtersbourg ; Me'- 

 langes physiques et chimiques, 1851, p. 32). 



( 51 ) p. 47. Middendorff, Bd. i. S. 166 compared with S. 179. " The limit 

 of the ground ice appears to have, in Northern Asia, two southerly inflexions, 

 one not deep on the Obi, and one very considerable on the Lena. The line 

 runs from Beresow on the Obi towards Turuchausk on the lenissei, then between 

 Witimsk and Oleminsk, on the right bank of the Lena, and then, eastward, 

 ascending to the north." 



( 52 ) p. 50. The principal passage in which the magnetic chain of rings is 

 spoken of is in the Platonic Ion, p. 533 D, E. ed. Steph. Subsequently, this 

 propagation of the attracting influence was mentioned by Pliny (xxxiv. 14) and 

 Lucretius (vi. 910), and also by Augustine (de Civitate Dei, xx. 4) and Philo 

 (de Mundi Opificio, p. 32 D. ed. 1691). 



(*) p. 51. Kosmos, Bd. i. S. 194 and 435, Anm. 32; Bd. ii. S. 293 

 295, 307322, 468, Anm. 59; and S. 481 482, Anm. 9193. 



( 54 ) p. 51. Compare Humboldt, Asie Centrale, t. i. p. xl. xlii., and Examen 

 crit. de 1'Hist de la Geographic, t. iii. p. 35. Eduard Biot, who, partly alone 

 and partly with the help of Stanislas Julien, has confirmed and enlarged, by 

 laborious bibliographic studies, Klaproth's researches on the antiquity of the 

 use of the magnetic needle in China, cites an older tradition, which, however, is 

 first found mentioned by writers of the first centuries of the Christian era, ac- 

 cording to which magnetic cars would have been used as early as under the 

 Emperor Hoang-ti. This celebrated monarch is supposed to have reigned 2600 

 years before our era (t. e. a thousand years before the expulsion of the Hyksos 

 from Egypt). Ed. Biot, " Sur la direction de 1'Aiguille aimantee en Chine," in 

 the Comptes rendus de 1'Acad. des Sciences, t. xix. 1844, p. 362. 



