►0 





OBSERVATIONS OF THE 









Date. 



Hour. 





Needle. 



No. 



Readings. 



Dip. 



1841, Aug. 17, 



10^—12^, A 



M. 



No. 2, 





40 



73° 38'.0 



u 



(( 





No. 2, poles reversed, 





40 



33.4 



(( 



(( 





Mean of No. 2, 





80 



35.7 



l( 



C( 





Mean of both needles, 





160 



73 35.3 





Observations repeated 



three Bods West of last Station. 





Date. 



Hour. 





Needle. 



No. 



Readings. 



Dip. 



1841, Aug. 17, 



3—5, P. 



M. 



No. 1, 





40 



73° 35'.3 



(( 



« 





No. 1, poles reversed, 





40 



30.1 



<i 



(( 





Mean of No. 1, 





80 



32.7 



«( 



(t 





No, 2, 





40 



32.1 



i> 



(( 





No. 2, poles reversed, 





40 



38.7 



(( 



<( 





Mean of No. 2, 





80 



35.4 



(( 



(( 





Mean of both needles. 





160 



73 34.1 





Observations repeated near the second Locality. 







Date. 



Hour. 





Needle. 



No 



Readings. 



Dip. 



1841, Aug. 18, 



8^—10, A. 



M. 



No. 1, 





40 



73° 30'.2 



(( 



(( 





No. 1, poles reversed. 





40 



38.5 



(( 



(( 





Mean of No. 1, 





80 



34.4 



(i 



<( 





No. 2, 





40 



40.6 



(( 



(( 





No. 2, poles reversed, 





40 



34.8 



ti 



<( 





Mean of No. 2, 





80 



37.7 



(( 



(( 





Mean of both needles, 





160 



73 36.0 





Observations 



repeated on the same Spot 









Date. 



Hour. 





Needle. 



No 



. Readings. 



Dip. 



1841, Aug. 18, 



10—12, A 



. M. 



No. 1, 





40 



73° 39'.9 



n 



<< 





No. 1, poles reversed. 





40 



29.6 



(( 



(( 





Mean of No. 1, 





80 



34.8 



(( 



t( 





No. 2, 





40 



34.4 



(( 



it 





No. 2, poles reversed. 





40 



41 .2 



(( 



11 





Mean of No. 2, 





80 



37.8 



(C 



it 





Mean of both needles, 





160 



73 36.3 



Mean of 800 read 



ings at Detroit 



, with both needles, 



. 



. . 



73 35.5 



The close agreement of the results in the five preceding series of observa- 

 tions shows that very little is gained, in point of accuracy, by multiplying the 

 observations beyond the usual number of a single series. 



