Ep ees] 
RU .L. E, 
Wiru the latitude by obfervation departed from 38° 52’, 
and that. by account arrived at 40° —’, and the departure 112, 
find the diftance as above 113, and with this diftance and the 
latitudes by obfervation, find the true difference of longitude 
2° 10 by Cafe III. of Mercator’s failing. 
Tue advantages expected to arife from the ufe of this inftru- 
ment are, firft, that no confiderable miftake can exift in the 
work, as the errors become obvious in proportion to their 
magnitude ; whereas in calculations, mifplacing a fingle figure 
will produce an error of the greateft confequence. Secondly, 
this method does not reft on tables or logarithms, which abound 
in errors of the prefs even in the beft editions, and are often the 
fource of much confufion. Thirdly, it will render the art of 
keeping a fhip’s reckoning eafily learned, and eafily prattifed. 
Many matters of fhips are perfons who have been raifed to that 
office from the loweft degree of feamen, who from want of 
capacity, or want of early opportunities, have acquired only a 
very fuperficial knowledge of navigation ; many who have been 
better educated difqualify themfelves by their riotous and diffo- 
lute lives for the practice of this intricate branch of fcience. 
The accidents of the fea, and other emergencies, frequently 
render it neceflary to commit the care of a fhip to an igno- 
rant failor. In all which cafes the methods of calculating a 
fhip’s courfe now in ufe can not be adopted or relied on with 
U fafety, 
