86 



Magnetic Dip iji the United States. 



gitudes have all been diminished seven minutes, which by my 

 observations is the error in the assigned longitude of Hudson. 

 Column fourth exhibits the observed dip, reduced to Jan. 1, 1840, 

 by assuming the annual motion to be — K8. Adopting for the 

 central position lat. 41° 22', Ion. 84° 54', we obtain the differen- 

 ces of latitude and longitude which furnish us the annexed equa- 

 tions of condition. 



The preceding equations furnish us, by the method of minimum 

 squares, with the following values: ^=3.5747, a;= + .01491, 

 ?/ = +.00262, and the direction of the isoclinal line is from N. 

 80° 1' W. to S. 80° V E. Computing from these data the dip 

 at the several stations, we obtain the differences given in the last 

 column above. When the observed dip is greater than the com- 



