460 



himself, at Paris, in the year 1818, with the contempora- 

 neous observations of M. KupfFer, at Casan. Not long af- 

 ter, the subject underwent a fuller investigation in the hands 

 of Humboldt; and, in the year 1827, an extensive system of 

 simultaneous observations was organized by that illustrious 

 philosopher for the purpose of elucidating it. At length, 

 in 1834, it was taken up by Gauss, and received a much 

 greater development. Gauss discovered that the irregular 

 changes of the declination were of continual occurrence ; 

 and that the synchronism, which had been previously ob- 

 served only in the larger changes, extended to the minutest 

 movements. In order to investigate the law of these syn- 

 chronous changes, and the locality and other circumstances 

 of the acting forces. Gauss arranged the extensive plan of 

 simultaneous observations at short intervals, which has been 

 already four years in operation, and in which almost every 

 country in Europe has been represented by some one or 

 more observers. 



Having taken part in this combined system in the year 

 1837, Prof. Lloyd was led to inquire, in the first place, whe- 

 ther this irregular fluctuation of the declination might not be 

 still more rapid than appeared from the observations hither- 

 to made ; and, secondly, whether these shorter oscillations (if 

 they existed) corresponded in distant places, and could 

 therefore be employed to determine differences of longitude. 



To investigate the first of these questions, a series of 

 observations was made in the month of September, 1837, at 

 very short intervals. The instrument employed was Gauss's 

 magnetometer ; and the magnet being in a state of continued 

 vibration, observations were taken at each succeeding maxi- 

 mum elongation, and therefore at the interval of a single 

 oscillation, — which, in the case of the bar employed, was 

 27^38. The mean of each successive pair of readings was 

 then taken, to eliminate the mechanical oscillation, and the 

 results projected in curves in the usual manner. On an 



