Natural History, Sec. 431 



very similar at the three places, but that the variations were far more 

 considerable at St, Petersburgh than at Nicolajew and Kasan. The 

 declination will be found to have been 



At Petersburgh. At Nicolajew. 



at 9 o'clock. . 9' 30" . . 4' 12" 



10 . . 15 45 . . 6 49 



11 . . 17 15 . . 9 34 



12 . . 37 15 . . 13 28 



Total 119'45 44' 33" 



and, as at St. Petersburgh, on the same day, between 7h. 40 m. A.M. and 

 2 h. 40 m. P.M., the declination amounted to 17 'J towards the west, 

 and at Nicolajew to 41', the above variation being nearly in the 

 ratio of two to one, the extent of the irregularity will accordingly 

 result. 



A needle, which at St. Petersburgh performs 300 oscillations in 

 1108'", makes at Nicolajew the same number within 964"; the ratio 

 of the squares is 1.3*2, and consequently much less than that of the 

 variation observed on the 5th of May ; the cause of the irregularity 

 has accordingly acted more powerfully at St. Petersburgh than at 

 Nicolajew. 



The remark of M. von Humboldt, that irregularities of the above 

 kind sometimes observe a sort of periodicity, being either followed 

 or preceded by irregular oscillations at the same hour for some days, 

 will be found confirmed by the following table of the progress of the 

 needle at the three places of observation on the 4th of May. 



Variation of the Deviation 



