MAGNETIC OBSERVATIONS. 11 



f"V 



of the Great Milischauer (Phonolith), inclination 67° 53'-5, 

 Teplitz inclination 67° 19 /, 5, and Prague inclination 66° 

 47 /# 6.* Simultaneously with the series of admirable com- 

 parative observations published with the fullest details of 

 the horizontal intensity, which were made in 1844 by Bra- 

 vais, in conjunction with Martins and Lepileur, and com- 

 pared at thirty-five stations, including the summits of Mont 

 Blanc (15,783 feet), of the Great St. Bernard (8364 feet), 

 and of the Faulhorn (8712 feet), the above-named physicists 

 made a series of inclination experiments on the grand plateau 

 of Mont Blanc (12,893 feet), and at Chamouni (3421 feet). 

 Although the comparison of these results showed that the 

 elevation of the soil exerted an influence in diminishing the 

 magnetic inclination, observations made at the Faulhorn and 

 at Brienz (1870 feet in elevation) showed the opposite result 

 of the inclination increasing with the height. The different 

 investigations on horizontal intensity and inclination failed 

 to yield any satisfactory solution of the problem. (Bravais, 

 Sur VIntensite du Magnetisme Terrestre en France, en Suisse, 

 et en Savoie, in the Annates de Chimie et de Physique, 3eme 

 serie, t. xviii., 1846, p. 225.) In a manuscript report by 

 Borda of his expedition to the Canary Islands in the year 

 1776, which is preserved at Paris in the Depot de la Marine, 

 and which I have been enabled to consult through the oblig- 

 ing courtesy of Admiral Rosily, I have discovered that Borda 

 was the first who made an attempt to investigate the influ- 

 ence of a great elevation on the inclination. He found that 

 the inclination was 1° 15 / greater at the summit of the Peak 

 of Teneriffe than in the harbor of Santa Cruz, owing un- 

 doubtedly to the local attractions of the lava, as I have oft- 

 en observed on Vesuvius and different American volcanoes. 

 (Humboldt, Voy. aux Regions Equinox., t. i., p. 116, 277, 

 288.) 



In order to try whether the deep interior portions of the 

 body of the earth influence magnetic inclination in the same 

 manner as elevations above the surface, I instituted an ex- 

 periment during my stay at Freiberg, in July, 1828, with all 

 the care that I could bestow upon it, and with a constant 



* I would again repeat that all the European observations of incli- 

 nation which have been given in this page have been reckoned accord- 

 ing to the division of the circle into 360 parts, and it is only in those 

 observations of inclination which I made myself before the month of 

 June, 1804-, in the New Continent, that the centesimal division of the 

 arc has been adhered to (Voy. aux Regions Equinox., t. iii., p. 615-623). 



