MAGNETISM. 161 



nation of the position of such magnetic axes of a mountain 

 would be of the greatest interest, if it could be ascertained 



obsidians of Quinche, north of Quito, as well as in the gray obsidian of 

 the Cerro de la Navajas of Mexico, large fragments with distinct poles. 

 The large collective magnetic mountains in the Ural chain, as Blagodat, 

 near Kuschwa, Wyssokaja Gora, at Nishne Tagilsk, and Katschkanar, 

 near Nishne Turinsk, have all broken forth from augitic or rather 

 uralitic porphyry. In the great magnetic mountain of Blagodat, which 

 I investigated with Gustav Rose, in our Siberian expedition, in 1829, 

 the combined effect of the polarity of the individual parts did not indeed 

 appear to have produced any determined and recognisable magnetic axes. 

 In close' vicinity to one another lie irregularly mixed opposite poles. A 

 similar observation had previously been made by Ennan (Reise urn die 

 Erde, Bd. i, a. 362). On the degree of intensity of the polar force in 

 serpentine, basaltic, and trachytic rock, compared with the quantity of 

 magnetic iron and protoxide of iron, intermixed with these rocks, as well 

 as on the influence of the contact of the air in developing polarity, which 

 had already been maintained by Gmelin and Gibbs, see the numerous and 

 very admirable experiments of Zaddach, in his Beobachtungen uber die 

 Magnetische Polaritdt des Basaltes und der Trachytischen Gestdne, 1851, 

 s. 56, 65 78, 95. A comparison of many basaltic quarries, made with a 

 view of ascertaining the polarity of individual columns which have stood 

 isolated for a long period, and an examination of the sides of these 

 columns which have been recently brdught in contact with the outer air 

 in consequence of the removal from individual masses of a certain 

 depth of earth, have led Dr. Zaddach to hazard the conjecture (see s. 

 74, 80) that the polar property, which always appears to be manifested 

 with the greatest intensity in rocks to which the air has been freely ad- 

 mitted, and which are intersected by open fissures, " diffuses itself from 

 without inwards, and generally from above downwards." Gmelin ex- 

 presses himself as follows in respect to the great magnetic mountain, 

 Ulu-utasse-Tau, in the country of the Baschkiri, near the Jaik : " The 

 sides which are exposed to the open air exhibit the most intense mag- 

 netic force, while those which lie under ground are much weaker" 

 (Reise durch Siberien, 17401743, Bd. iv, s. 345). My distinguished 

 teacher, Werner, in describing the magnetic iron of Sweden, in hia 

 lectures, also spoke of " the influence which contact with the atmo- 

 sphere might have, although not by means of an increased oxidation, in 

 rendering the polar and attracting force more intense." It is asserted 

 by Colonel Gibbs, in reference to the magnetic iron mines at Succas- 

 suny, in New Jersey, that "the ore raised from the bottom of the mine 

 has no magnetism at first, but acquires it after it has been some time 

 exposed to the influence of the atmosphere" (On the connexion of Mag- 

 netism and Light, in Silliman's American Journal of Science, vol. i, 1819, 

 p. 89). Such an assertion as this ought assuredly to stimulate obser- 

 vers to make careful and exact investigations ! When I drew attention 

 in the text (see page 160), to the fact that it was not only the quantity 

 of the small particles of iron which we're intermixed in the stone, but 

 Mso their relative distribution (their position) which ac^ed as the 19- 

 VOL. V. M 



