MAGNETIC DIP IN THE UNITED STATES. 



291 



Magnetic Dip at Mackinac, Michigan. Latitude 45° 51' N.; Longitude 84° 41' W. 

 Place of observation a quarter of a mile south-west of the fort. 



Date. 







Hour. 





Needle. 



No. 



Readings. 



Dip. 



1841, Aug. 



21, 



8- 



-10, A. 



M. 



No. 1, 





40 



76° 33'.4 



cc 







(( 





No. 1, poles reversed, 





40 



42.2 



(( 







<< 





Mean of No. 1, 





80 



37.8 



(( 







<< 





No. 2, 





40 



43.4 



(( 







(( 





No. 2, poles reversed, 





40 



35.2 



(( 







(( 





Mean of No. 2, 





80 



39.3 



(C 







<( 





Mean of both needles. 





160 



76 38.5 









Observations 



repeated on the same Spot. 









Date. 







Hour. 





Needle. 



No. 



Readings. 



Dip. 



1841, Aug. 



21, 



10- 



-12, A. 



M. 



No. 1, 





40 



76° 43'.0 



(( 







i( 





No. 1, poles reversed. 





40 



37.6 



(( 







<( 





Mean of No. 1, 





80 



40.3 



(( 







(t 





No. 2, 





40 



34.6 



(< 







(< 





No. 2, poles reversed. 





40 



40.5 



<( 







(( 





Mean of No. 2, 





80 



37.5 



(( 







<c 





Mean of both needles, 





160 



76 38.9 





Observations repeated fifteen Rods North-East of last Station. 





Date. 







Hour. 





Needle. 



No 



. Readings. 



Dip. 



1841, Aug. 



21, 



2- 



-3i, P. 



M. 



No. 1, 





40 



76° 36'.3 



t( 







n 





No. 1, poles reversed. 





40 



41 .5 



(( 







(t 





Mean of No. 1, 





80 



38.9 



C( 







11 





No. 2, 





40 



38.7 



<( 







<t 





No. 2, poles reversed. 





40 



32,0 



(( 







(< 





Mean of No. 2, 





80 



35.4 



i( ' 







(t 





Mean of both needles. 





160 



76 37.1 









Observations 



repeated on the same Spot. 









Date. 







Hour. 





Needle. 



No 



. Readings. 



Dip. 



1841, Aug. 



21, 



H- 



-5, P. 



M. 



No. 1, 





40 



76° 39'.4 



n 







(C 





No. 1, poles reversed. 





40 



31 .4 



(( 







(< 





Mean of No. 1, 





80 



35.4 



(< 







(C 





No. 2, 





40 



33.3 



C( 







(( 





No. 2, poles reversed, 





40 



38.4 



(( 







(( 





Mean of No. 2, 





80 



76 35.8 



(I 







C( 





Mean of both needles. 





160 



76 35.6 



Mean of 640 reading! 



3 at Mackinac, with both needles, . 



. 



. 



76 37.5 



VIII. 



,— 3y 

















