INTRODUCTION. 51 



plan. The extension necessary for any degree of 

 latitude, is found, in the tables of increasing lati- 

 tudes, (Mendoza's tables, p. 651. et seq. Meri- 

 dional Parts,) expressed in minutes of longitude, 

 whence the magnitudes of the single degrees, or of 

 half and quarter degrees, are obtained by an easy 

 subtraction. 



The degrees of latitude having been inserted 

 and divided, the first thing is, to mark upon the 

 chart the complete course of the ship, laying down, 

 as fundamental points, those which have been as- 

 tronomically determined, and then marking the 

 ship's way between them, according to the log- 

 book. At every corner point of this broken line, 

 the time is to be noted at which the ship was in 

 that station. 



You then set out (from the first station) the 

 rhumb, given in degrees, of the first object to the 

 left, and from this line, by means of a good pro- 

 tractor, all the other angles that have been mea- 

 sured. To every line of sight the letters marked 

 in the sketch of the coast are annexed. Then you 

 proceed to the second station, and lay down from 

 that, in the same manner, the angles measured. 

 The intersection of the corresponding lines of 

 sight gives the point where each object is. The 

 angles at the third station give partly new deter- 

 minations, partly confirmations and corrections of 

 the points fixed by the two preceding measure- 

 ments. Meantime, the remarks are inserted where 



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