XXVI NOTES. 



creasing height results from the comparison of the Silla de Caracas (8105 feet 

 above the sea; force 1-188) with the harbour of La Guayra (height 0; force 

 1-262), and with the town of Caracas (height 2484 feet; force 1-209); from 

 the comparison of the town of Santa F<$ de Bogota (height 8190 feet; force 

 1-147) with the Chapel of Nuestra Senora de Guadalupe (height 10,128 feet. 

 force 1-127), placed, like a swallow's nest, on a steep precipice overhanging the 

 town, and in the closest proximity to it; from the comparison of the volcano of 

 Purace (height 13650 feet; force 1-077) with the mountain-village of Pnraee 

 (height 8136 feet; force 1-087), and with the neighbouring town of Popayan 

 (height 5466 feet; force 1'117); and from the comparison of the town of Quito 

 (height 8952 feet; force 1-067) with the village of San Antonio de Lulum- 

 bamba (height 7650 feet; force 1*087), situated in an adjacent ravine, and 

 exactly on the geographical equator. An opposite result was derivable from the 

 most elevated site at which I ever made magnetic experiments of vibration, i. e. 

 at a height of 14,960 feet on the side of the long-extinct volcano of Antisana, 

 opposite Chussulongo. The observations had to be made in a large cave, and the 

 great increase of force was no doubt caused by a local attraction of the rock 

 (trachyte), as was the case in experiments made by Gay-Lussac and myself 

 on the margin of the crater of Vesuvius, and in the crater itself. In the cave 

 of Antisana I found the magnetic force raised to 1-188, it being scarcely 1-068 

 on the neighbouring elevated, but yet much lower, table-lands. The intensity of 

 the force at the Hospice on the St. Gothard (1-313) was greater than that at 

 Airolo (1-309), though less than at Altorf (1-322); but the force at the Ursern 

 Loch (1-307) was less than at Airolo. So also Gay-Lussac and myself found 

 the intensity of the force at the Hospice on Mont Ceiiis 1-344, that at Lans le 

 iourg, at the foot of Mont Cenis, 1-323, and at Turin 1-336. The greatest 

 anomalies, as might naturally have been anticipated, were presented by the still 

 active volcano of Vesuvius. When, in 1805, we found the magnetic force 1-274 

 at Naples, and 1-288 at Portici, we found it increased to 1-302 at the hermitage 

 of San Salvador, and diminished to 1-193 (lower than any place in the whole 

 district) in the crater of Vesuvius. Ferrugineous matter in the lavas, proximity 

 of magnetic poles in particular pieces, and the probably, on the whole, weakening 

 effect of the heating of the ground, all contribute to produce the most opposite 

 local disturbances. Compare my Voyage aux Kegions dquinoxiales, t. iii. p. 

 619626, and Mem. de la Socie'te' d'Arcueil, t. i. (1807) p. 1719. 



( I12 ) p. 103. Kupffer's observations were not made at the summit of Mount 

 Elbrouz, and only apply to the difference of elevation (4500 feet) between two 

 stations, the Bridge of Malpa, and the slope of the Mountain of Kharbis, situated 

 at no inconsiderable distance from each other in a horizontal line. On the ob- 



