376 Astronomical and Nautical Collections. 



Use of the Table. 

 Find by observation the greatest disturbance produced by tfic 

 ship's action on the compass in any given part of the globe, and 

 subtract from the logarithm of its sine the number in the last 

 column of the table opposite to the given dip, the difference will 

 be the logarithm of the constant multiplier for that ship ; and if 

 it be added to the tabular number for any other place, or for 

 any other position of the ship, it will give the logarithmic 

 sine of the correction required on account of the permanent 



attraction. 



Example. 



Supposing the utmost disturbance in the Isabella to be 5° 40', 

 when the dip, is 74° 23' ; the numbers of the last column for 

 74° and 75° being 1.6043 and 1.6268, the difference .0223 be- 

 comes, for 23', .0085, and for 74° 23' we have 1.6128, which, 

 subtracted from 8.9945, the logarithmic sine of 5° 40', leaves 

 7.3817, the logarithm of the constant multiplier for the Isabella ; 

 then the greatest tabular number for the dip 86° being 2.1596, 

 adding this to 7.3817, the sum 9.5413 is the logarithmic sine of 

 20° 21', the greatest disturbance where the dip is 86°; and 

 when the ship's head, or the neutral point, or point of change, 

 appears by the compass to be NE., or 4 points from the mag- 

 netic North, the tabular number at 74° 23' will be 1.4623, and 

 the logarithmic sine 8.8440, answering to 3° 58'; and at 86°, 

 2.0091, giving the logarithmic sine 9.3908, and the angular 

 correction 14° 14', so that the true situation of the ship will in 

 this instance be more than a point further from the magnetic 

 North than the compass indicates ; it is also obvious, that the 

 correction will be very different from that which would be re- 

 quired, if the actual bearing of the ship's head were NE. or NW. 

 13. According to the observations collected and computed 

 by the laborious and accurate Professor Hansteen, we have the 

 actual intensity of the magnetic force in different places, as in 

 the following table. 



