MAGNETIC DIP IN THE UNITED STATES. 287 



which we obtain the differences between the observed and computed dips, as 

 given in the last column above. The dip obtained August, 1840, by observa- 

 tions in different azimuths, was 72° 49'.6, being 1'.2 greater than is computed 

 from the above data; the dip, May, 1841, by Mayer's method, was 72° 47'. 7, 

 being 0'.9 less than we obtain from the same data. Mean error of observations 

 by the usual method + O'.l, a quantity so small that it has been neglected. 

 The following observations were made by the usual method. 



Magnetic Dip at Brooklyn, Ohio. Latitude 41° 30' N.; Longitude 81° 43' W. 



Place of observation one mile west of Ohio city. 



Date. 







Hour. 





Needle. 



No. 



Readi 



ngs. 





Dip. 



1841, April 



23, 



11- 



-1,P. 



M. 



No. 1, 





40 





73' 



' 10.2 













No. 1, poles reversed, 





40 







18.9 













Mean of No. 1, 





80 







14.6 













No. 2, 





40 







19.7 













No. 2, poles reversed, 





40 







16.3 













Mean of No. 2, 





80 







18.0 













Mean of both needles, 





160 





73 



16.3 



Magnetic Dip at Tallmadge, Ohio. Latitude 41° 6' N.; Longitude 81° 27' W. 

 Place of observation nearly the same as formerly. 



Date. 





Hour. 





Needle. 



No. 



Readi 



:ngs. 



Dip. 



U, April 



26, 



8—10, A. 



M. 



No. I, 





40 





72° 55'.6 











No. 1, poles reversed. 





40 





49.1 











Mean of No. 1, 





80 





52.4 











No. 2, 





40 





52.4 











No. 2, poles reversed, 





40 





63.5 











Mean of No. 2, 





80 





58.0 











Mean of both needles, 





160 





72 55.2 



Magnetic Dip at Cleveland, Ohio. Latitude 41° 30' N.; Longitude 81° 41' W. 

 Place of observation one mile east of the city. 



■Date. Hour. Needle. No. Readings. Dip. 



1841, Aug. 12, 4—1, P. M. No. 1, 40 73° 7'.9 



" •' No. 1, poles reversed, 40 2 .0 



" " Mean of No. 1, 80 5 .0 

 VIII. — 3 X 



