REPORT ON THE MAGNETISM OF THE EARTH. 



109 



morning *, yet his observations and remarks are of great value 

 as pointing out the annual oscillations of the needle f. Since 

 this, the diui-nal variation has been very generally observed, 

 but by no one with greater care and perseverance than by the 

 late Colonel Beaufoy ;}:. 



In order to determine whether the course of the diurnal va- 

 riation is influenced by the elevation of the place of observation, 

 the zealous and indefatigable De Saussure undertook a series 

 of observations on the Col du Geant, nearly 11,300 feet above 

 the level of the sea. This series, after incurring much personal 

 inconvenience and even risk in that region of snow and of storms, 

 he completed ; and he has compared the results with observa- 

 tions which he made immediately before and after at Chamouni 

 and Geneva. From this comparison it appears that the course 

 of the diurnal variation was nearly the same on one of the 

 highest mountains, in a deep and narrow valley at its foot, and 

 in the middle of a plain or of a large valley. The times of the 

 maxima, east and west, are in each case nearly those previously 

 determined by Canton, these maxima occurring rather later on 

 the Col du Geant than at the other stations. Excluding in all 

 cases the results where extraordinary causes appear to have 

 operated, the extent of the diurnal variation at Chamouni ex- 

 ceeds that at Geneva and also that on the Col, the two latter 

 being very nearly the same. The observations, however, are, 

 as Saussure very justly remarks, nuich too limited to give cor- 

 rect means §. 



5. The Dip of the Magnetic Needle. — Norman having found 

 with different needles, and with one in particular on the con- 

 struction of which he had bestowed much pains, that although 

 perfectly balanced on the centre previously to being touched 

 by the magnet, after this operation the north end always de- 

 clined below the horizon, devised an instrument by which he 



• Journal de Physique, Mai 1792, torn. xl. p. 345. f Ibid. p. 348. 



Many of the results of Colonel Beaufoy 's observations are published in the 



Edinburgh PhilosophicalJoumal, vols. i. ii. iii. iv. and vii. 



§ Saussure, Voyayes dans les Alpes, torn. iv. p. 302 au p. 312. 

 does not give the mean results, I insert them here. 



As Saussure 



Time of absolute maximum. Time of second maximum. 



Geneva 



Cliamouni ... 

 Col du Geant 



East. 



h m 



7 56 A.M. 



7 34 



8 09 



West. 



h m 



1 09 P.M. 



1 41 



2 00 



East. 



6 26 P.M. 



7 44 

 5 51 



West. 



h m 

 11 17 P.M 



10 46 

 10 17 



Extent of Elevation 

 diurnal above the 

 change. sea. 



15 42 

 17 06 

 15 43 



Feet. 



1305 



3453 



11274 



