

Sect. III.] 



HYDROGRAPHlt. 



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to the accuracy of the survey if landings be occasionally 

 made, and the stations be critically determined by astro- 

 nomical observation, i. e., by latitudes and chronomete 

 and the positions connected with the rest of the \^ork. 



30. It is not necessary to be provided with a regular 

 chart for this purpose ; the projection may proceed as you 

 advance. Thus, consider how the coast runs, and draw a 



line along the paper to represent the meridian at starting ; 

 set off on this a degree of latitude according to the scale 

 on Avhich the survev is to nroceed, 1 inch or IJ inchpB 

 to the mile, or more or less according to circurastanceSj 



and begin at once to lay off the bearings and angles. K% 



you take up other stations proceed to throw out meridians 

 and parallels in the manner described in 

 No. 10. A chart upon this projection will be found easy 

 of construction and more satisfactory than any other ; and 



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when the survey does not extend over more than 8 or 

 10 degrees of latitude is sufficiently correct. In laying 

 off bearhigs upon it, it must be borne in mind that they 

 are to be projected with reference to the meridian passing 

 through the spot. Mercator's projection, in which the 

 meridians are all parallel, and which is in such general 

 use in the navy, except in very low latitudes, is not adapted 

 to the purposes of a survey, as the bearings and the pro- 

 traction will never agree together nor with the observed 



latitude and longitude of the stations. 



With reference to the longitude I may remark, that the 

 absolute longitude of the place is not required, but it is 

 necessary to determine the difference of meridians as you 



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proceed ; and these should afterwards be compared with 

 some well-determined meridian. I may observe here, 





