96 COSMOS. 



Germany.* These observations extended from the level of 

 the sea to an elevation of 15,944 feet, and therefore to the 

 very limits of 'perpetual snow, but the greatest heights did 

 not afford me the most reliable results. The most satis- 

 factory were obtained on the steep declivity of the Silla de 

 Caracas (8638 feet), which inclines toward the neighboring 

 coasts of La Guayra; the Santuario de Nostra Senora de 

 Guadalupe, which rises immediately over the town of Bogota, 

 upon the declivity of a steep wall of limestone rock, with a 



* A diminution of the intensity with the height is shown in ray 

 observations from the comparisons of the Silla de Caracas (8638 feet 

 above the- sea, intensity 1-188) with the harbor of Guayra (height 

 feet, intensity 1-262) and the town of Caracas (height 2648 feet, in- 

 tensity 1*209) ; from a comparison of the town of Santa Fe de Bogota 

 (elevation 8735 feet, intensity 1*147) with the chapel of Neustra Se- 

 nora da Guadalupe (elevation 10,794 feet, intensity 1*127), which 

 seems to hang over the town like a swallow's nest, perched upon a 

 steep ledge of rock ; from a comparison of the volcano of Purace (ele- 

 vation 14,548 feet, intensity 1*077) with the mountain village of Pu- 

 race (elevation 8671 feet, intensity 1*087) and with the neighboring 

 town of Popayan (elevation 5825 feet, intensity 1*117); from a com- 

 parison of the town of Quito (elevation 9541 feet, intensity 1*067) 

 with the village of San Antonio de Lulumbamba (elevation 8131 feet, 

 intensity 1*087), lying in a neighboring rocky fissure directly under 

 the geographical equator. The oscillation experiments, which I made 

 at the highest point at which I ever instituted observations of the kind, 

 namely, at an elevation of 15,944 feet, on the declivity of the long- 

 since extinct volcano of Antisana, opposite the Chussulongo, were 

 quite at variance with this result. It was necessary to make this ob- 

 servation in a large cavern, and the great increase in the intensity 

 was no doubt the consequence of a magnetic local attraction of the 

 trachytic rock, as has been shown by the experiments which I made 

 with Gay-Lussac within, and on the margin of, the crater of Vesuvius. 

 I found the intensity in the Cave of Antisana increased to 1*188, 

 while in the neighboring lower plateau it was scarcely 1*068. The 

 intensity at the Hospice of St. Gotthard (1*313) was greater than that 

 at Airolo (1*309), but less than that at Altorf (1*322). Airolo, on the 

 other hand, exceeded the intensity of the Ursern Lake (1*307). In 

 the same manner Gay-Lussac and myself found that the intensity was 

 1*344 at the Hospice of Mont Cenis, while at the foot of the same 

 mountain, at Lans le Bourg, it was 1*323, and at Turin 1*336. The 

 greatest contradictions were necessarily presented by the burning vol- 

 cano of Vesuvius, as we have already- remarked.- While in 1 805 the 

 terrestrial force at Naples was 1*274, and at Portici 1*288, it rose in 

 the Monastery of St. Salvador to 1*302; while it fell in the crater of 

 Vesuvius lower than any where else throughout the whole district, 

 namely, to 1*193. The iron contained in the lava, the vicinity of 

 magnetic poles, and the heat of the soil, which probably has the effect 

 of diminishing this force, combined to produce the most opposite local 

 disturbances. See my Voyage aux Regions Equinox iales, t. iii., p. 619^^ 

 626, and Mem. de la Societe d'Argueil, t. i., 1807, p. 17-19. 



