LIETJT.-GENEEAL SABINE ON TEEBESTEIAL MAGNETISM. 



489 



Iderived from the deviations of the Declination. 

 )J 



Columns 4 and 5 exhibit the same particulars at Simon's Bay. In column 6 is placed 

 the mean deviation at the two stations, and in column 7 the mean deviation applied to 

 — 53° 0' taken as an approximate mean dip common to both stations. In columns 

 8 and 9 are shown the values of ^ and ^ on each point of the compass, ^ being the azimuth 

 of the ship's head by the standard compass, and ^ tabular or calculated values derived 

 from the observed deviations of the declination on the same points. Column 10 contains 

 the dips on the different points computed by the several constants, which are as follows : — 



B=a tan fl= --04411 

 J=1-2D=+-9875J 



~ ~*~ I derived from the deviations of the Dip in column 7. 



(?=+0-9936j ^ 



And, finally, in column 11 are shown the differences between the observed and the com- 

 puted deviations. 



The values of c and d have been computed by equation (9) (Philosophical Transactions, 

 1843, p. 148) on all points excepting north and south ; and on those points by equation 

 (10). The computed dips by equation (13) on all points excepting east and west, on 

 which points equation (12) has been substituted. 



The Table for the correction of the deviations of the dip in the third year's survey has 

 been formed by computing, by means of the above constants, the deviations in dips suc- 

 cessively of —53°, —59°, and —65°, and interpolating the intermediate values. 



Table III. 



2. In the ' Terror' — ^The constants c and A in this ship have been derived from the 



