[ 8 77 ] 
courfe defigned, and finding the fhip’s true place, as 
near as may be, by what the mariners call the dead- 
reckoning. 
The particular ufes will be beft explained by ex- 
amples ; for inftance, in the fouthern parts of the 
great Atlantic ocean, beginning with the coaft of Bra- 
zil and Patagonia, and proceeding to the fouth of 
the Cape of Good Hope into the Indian ocean, as 
far as the common tracks of our Eaft-India fhips 
extend, the variation lines have appeared to be, for 
the moft part, diredted northward and fouthward ; 
whence, in moft places of that great body of waters, 
if the latitude and variation be found by celeftial ob- 
fervations, the longitude will be obtained by the lines 
on the chart; the great ufefulnefs of which has been 
attefted to the writers, by many perfons who have, 
fuccefi fully to themfelves, practically applied the laft 
conftrudted Chart, to corredt their dead- reckoning 
on that long pafiage. 
Indeed, where the variation lines run nearly eaft- 
ward and weftward, as has appeared in the Atlantic 
ocean, from the weft coaft of Europe to the eaft 
coaft of North America, no affiftance towaid ob- 
taining the longitude can be derived from them ; but 
as it frequently happens, within thofe limits, that 
meridian obfervations, for determining the latitude, 
cannot be obtained, efpecially about Newfoundland > 
then, if a good obfei vation of the variation can be 
taken, at any time of the day, the latitude may be 
nearly afcertained by the lines on theC hart. 
Secondly, The advantage that will arife by extend-^ 
ing the variation line^ over the land, as well as fea, 
will be the confirmation of thofe drawn over the 
waters 3 
