APP. N'^ IX.] MAGNETICAL OBSERVATIONS. 



545 



So that from this Table it would seem, that in Captain 

 Ross's voyage, the intensity of the magnetic force was 

 the greatest where the dip was the greatest, and gene- 

 rally, though not uniformly, increased as the dip in- 

 creased. In London, where the dip is 70°.34'5 12.45 

 vibrations of the dipping needle, when in the meridian, 

 were performed in a minute ; and in Baffin's Bay, 

 where the dip was 86^9', 1'3.8 vibrations were per- 

 formed in the same interval. 



Hence the magnetic force in the two positions, appears to be 

 as the square of 12.45, or 155, the number of vibrations 

 in London, to the square of 13.8 or 190, the number 

 performed in Baffin's Bay. These observations would 

 have been much more valuable, had they been accom- 

 )5anied by a corresponding number of observations per- 

 formed in the same situation by a horizontal needle. 



(d.) Captain Ross informs us, in the Appendix to his " Voy- 

 age of Discovery," that in his experiments on local at- 

 traction, the magnetic anomaly or " deviation appeared 

 to be materially affected by heat and cold, as well as 

 by atmospheric humidity and density ;" and that the 

 direction of the wind seemed to have an irregular effect 



on the deviation. 



VOL. ir. 



"SI m 



