MAGNETIC DIP IN THE UNITED STATES, 



293 



Magnetic Dip at Gros Cap, Canada. Latitude 46° 32' N.; Longitude 84° 43' W. 



Date. 





Hour. 





Needle. 



No 



Readi 



ngs. 



Dip. 



1841, Aug, 



26, 



1—3, P. 



M. 



No. 1, 





40 





77° 4'.8 



(( 









No. 1, poles reversed, 





40 





8.9 



(( 









Mean of No. 1, 





80 





6.9 



(i 









No. 2, 





40 





6.9 



(C 









No. 2, poles reversed, 





40 





0.4 



1 " 









Mean of No. 2, 





80 





3.6 



(C 









Mean of both needles, 





160 





77 5.3 



The difference in the dip observed at Gros Cap, and at Fort Brady, is 24'.4, 

 whereas the dip at the two places might have been anticipated to be nearly 

 the same. At the Sault the red sandstone appears on the surface of the earth, 

 and contains a large per centage of iron. 



Magnetic Dip at South Manitou, Michigan. Latitude 45° 5' N.; Longitude 85° 38' W. 



Place of observation near the eastern shore, about the middle of the island, 

 as regards north and south. 



Date. 





Hour. 





Needle. 



No. 



Readings. 





Dip. 



1841, Aug. 



31, 



9— lOi, A. 



M. 



No. 1, 





40 



75 



= 55'.4 











No. 1, poles reversed. 





40 





62.6 











Mean of No. 1, 





80 





59.0 











No. 2, 





40 





67.5 











No. 2, poles reversed, 





40 





51 .9 











Mean of No. 2, 





80 





59.7 











Mean of both needles. 





160 



75 



59.3 



Magnetic Dip at Chicago, Illinois. Latitude 41° 53' N.,- Longitude 87° 44' W. 

 Place of observation one mile north of the town. 



Date. 



Hour. 





Needle. 



No 



Readings. 





Dip. 



1841, Sept. 2, 



8i_10^, A. 



M. 



No. 1, 





40 



72 



° 50'.6 









No. 1, poles reversed, 





40 





47.0 









Mean of No. 1, 





80 





48.8 









No. 2, 





40 





47.8 









No. 2, poles reversed. 





40 





46.5 









Mean of No. 2, 





80 





47.1 









Mean of both needles, 





160 



72 



48.0 



