[ 55 s ] 
pofe to (hew how high the errors can ever arile j and 
how they may, if it is thought needful, be nearly 
eftimated and corrected. 
Write down, in a vacant fpace at the bottom of 
the map, a table of the errors of equidiftant parallels, 
as from live degrees to five degrees of the whole lati- 
tude ; and having taken the mean errors, and dimi- 
nifhed them in the ratio of radius to the fine of the 
mean inclination of the line of diftance to the meri- 
dian, you lhall find the correction required j remem- 
bering only to diftinguifti the diftance into its parts 
that lie •within and without the fphere, and taking 
the difference of the correfpondent errors, in defebl 
and in excefs. 
But it was thought needlefs to add any examples ; 
as, from what has been faid, the intelligent reader 
will readily fee the ufe of fuch a table j and chiefly 
as, whenever exaCtnefs is required, it will be more 
proper, and indeed more expeditious, to compute 
the diftances of places by the following canon. 
Multiply the produdl of the cofines of the two given 
latitudes by the fquare of the fne of half the difference 
of longitude j and to this product add the fquare of 
the fine of half the difference of the latitudes ; the 
fquare root of the fumjhall be the fine of haf the arc 
of a great circle between the two places given. 
Thus, if we are to find the true diftance from 
one angle of our map to the oppolite, that is, from 
S to Q, the operation will be as follows : 
5 
L. fin. 
