MAGNETIC DIP IN THE UNITED STATES. 



299 



September 21. — One end of No. 2 was rubbed on a hone, to reduce the in- 

 equality in the weight of the arms. 



Magnetic Dip at Alton, Illinois. Latitude 38^ 54' N.; Longitude 90° 4' W. 

 Place of observation in Middletown, a half mile from the landing-. 



Date. 



Hour. 





Needle. 



No. 



Readings. 





Dip. 



1841, Sept. 22, 



8—10, A 



M. 



No. 1, 





40 



69 



' 24'.2 



(( 



(C 





No. 1, poles reversed, 





40 





36.3 



(< 



t( 





Mean of No. 1, 





80 





30.2 



(( 



IC 





No. 2, 





40 





37.3 



«( 



t( 





No. 2, poles reversed, 





40 





43.6 



i( 



<c 





Mean of No. 2, 





80 





40.4 



<c 



(( 





Mean of both needles. 





160 



69 



35.3 





Observations 



repeated 



six Bods Last of the last Station. 







Date. 



Hour. 





Needle. 



No 



Readings. 





Dip. 



1841, Sept. 22, 



10—12, 



M. 



No. 1, 





40 



69° 36'.4 



<< 



<( 





No. 1, poles reversed. 





40 





23.0 



(( 



(( 





Mean of No. 1, 





80 





29.7 



<( 



« 





No. 2, 





40 





40.2 



(( 



<( 





No. 2, poles reversed. 





40 





37.8 



it 



(t 





Mean of No. 2, 





80 





39.0 



(( 



(( 





Mean of both needles, 





160 



69 



34.3 



Mean of 320 reac 



lings of both needles, . 



^ • • • 



. 



. 



69 



34.8 



Magnetic Dip at Upper Jilton, Illinois. Latitude 38° 55' N.; Longitude 90° 3' W. 



Place of observation a few rods east of the college. 



Date. 



Hour. 





Needle. 



No. 



Readings. 



Dip. 



1841, Sept. 22, 



2—4, P. 



M. 



No. 1, 





40 



69° 34'.0 





n 





No. 1, poles reversed. 





40 



46.5 





(( 





Mean of No. 1, 





80 



40.3 





(( 





No. 2, 





40 



49.2 





(C 





No. 2, poles reversed, 





40 



50.0 





(( 





Mean of No. 2, 





80 



49.6 





(( 





Mean of both needles. 





160 



69 44.9 





Observations 



repeated 



a few rods south of former station. 





Date. 



Hour. 





Needle. 



No 



Readings. 



Dip. 



1841, Sept. 25, 



2—4, P. 



M. 



No. 1, 





40 



69° 39'.8 



t( 



(( 





No. 1, poles reversed, 





40 



50.8 



VIII. — 4 



A 













