[ 575 ] 
compafs of eleven days, between March 9th and 
20th, I had the curiofity to compare them together. 
Setting afi.de any errors in the common method of 
keeping a fhip’s reckoning, and fuppofing us not to 
be affedted by currents during this time, the fame 
difference ought to have been found between all the 
longitudes by account, and the longitudes deduced 
from the Moon, or the fame error of the common 
account ought to have refulted from all the obferva- 
tions. The mean error of account from all the twelve 
obfervations is 5 0 20', by which we were really 
more to the weft than our account made us. And 
comparing each particular error of account with this 
quantity, the difference between them, in any of the 
twelve obfervations, fcarce exceeds a degree ; whence 
we may fuppofe, that the longitude was deduced truly 
from every one of thefe twelve obfervations, within 
the compafs of lefs than ii-°. 
I have fet them down in the following table, the 
error of the common account, and the difference be- 
tween 5 0 2', the mean quantity of it, and each 
particular error of account, which, except in the firft 
and laft obfervations, does not exceed J*°. The laft 
obfervation, which differs moft from the medium, 
was taken in fome hafte, on account of the pofition 
of the fails of the fhip, which did not allow a mean 
uninterrupted view of the ftar ; neverthelefs, as I was 
tolerably fatisfied with the obfervation at the time, 
and as it does not materially differ from the others, I 
did not think proper to rejed it, 
*761. 
Vol. LII 
