xlviii NOTES. 



usually at night in this month to from 2' 27" to S', increased during the course 

 of the aurora, progressively, and without any considerable oscillations, to a 

 difference of 26' 28". The deflection was least at 9 h 12 m , when the auroral 

 light was most intense. In the horizontal magnetic force, we found during the 

 aurora 97"73 for 21 vibrations, and at 21 h 50 m therefore long after the 

 termination of the aurora, which had ended at 14 h 10 m 97*'17 for the same 

 number of vibrations. The temperature of the room in which the vibrations of 

 the small needle were observed was, in the first instance, 3'2 Cent., and in the 

 second, 2'8. The intensity had therefore diminished a little during the aurora. 

 There were no coloured rings round the moon." (Extract from my magnetic 

 journal.) Compare Hansteen, S. 459. 



( 221 ) p. 159. Sabine, On Days of Unusual Magn. Disturbances, Pt. I. p. xviii. 

 "M. Bravais conclut des observations de Laponie qne 1'intensite horizontale 

 diminue pendant la pe'riode la plus active du phenomene de 1'aurore bore'ale." 

 (Martins, p. 461.) 



(-") p. 1 59. Delesse, " Sur 1'Association des Mine'raux dans les Roches qui 

 ont un pouvoir magne'tique e'leve'," in the Comptes rendus de 1'Acad. des So. 

 t. xxxi. 1850, p. 806; and Annales des Mines 4 e se'rie, t. xv. (1849) p. 130. 



( 223 ) p. 159. Reich, on Mountain and Rock Magnetism in Poggend. Ann. 

 Bd. Ixxvii. S. 35. 



( K4 ) p. 160. When, in 1796, I filled the post of Superintendent of Mines in 

 the Fichtelgebirge in Franconia, and discovered the effects of the remarkable 

 Serpentine Mount (the Haidberg), which at some places affects the declination 

 of needles 24 feet distant, this question was raised. (Intelligenz-Blatt der all- 

 gem. Jenaer Litteratur-Zeitung, Dec. 1796, No. 169, S. 1447, and March 

 1797, No. 38, S. 323326; Gren's Neues Journal der Physik, Bd. iv. 1797, 

 S. 136; and Annales de Chimie, t. xxii. p. 47.) I thought I had found that 

 the magnetic axes of the mountain were directly inverted in relation to those of 

 the Earth; but, according to the investigations of Bischoff and Goldfuss (Beschrei- 

 bung des Fichtelgebirges, Bd. i. S. 196), there were indeed recognised in 1816 

 magnetic axes traversing the Haidberg, and presenting opposite poles at the op- 

 posite declivities, but yet the azimuthal direction of the axes differed from that 

 which I had assigned. The Haidberg consists of green serpentine rock, partly 

 passing into choride-slate and hornblende-slate. In South America we found at 

 the village of Voysaco, in the Cordillera of Pasto, dykes of clay porphyry, and, 

 in the ascent of Chimborazo, groups of columnar trachyte, which affected the 

 needle at three feet distance. I was struck by finding in the black and red obsi- 

 dians of the Quinche, north of Quito, as well as in the grey obsidian of the Cerro 

 de las Navajas, of Mexico, large fragments having decided poles. All the con- 



