[ 5 6 7 ] 
and feems better calculated for determining fuperficial 
and linear meafures, than any other that has occurred 
to me. 
This Gentleman illuftrates his theory with ex- 
amples juftly intended to point out the quantity of 
error, that will happen in a large extent. 
For inftance ; Between latitudes io° and 6 o° N. 
and containing no degrees difference of longitude, 
Mr. Murdoch computes the diftance at 5-794, miles ^ 
which, upon the arc of a great circle, is found to be 
74.77, or by other methods 574.62 ; fo that the dif- 
ference is only 1 17, or at moft 132 miles in fo great 
an extent, and to an high latitude ; and the higher 
the latitude the greater the error is like to be, where- 
ever middle latitude is concerned. 
His courfes alfo agree very nearly with computa- 
tions made from the tables of meridional parts. 
In example the firfl they are the very fame : 
In example the ad they agree to half a minute : 
In example the 3d they vary i°4 / , on account of 
the high latitudes, which extend from 56° to 8o°N. 
However, I do not efteem this method fo fimple, 
eafy, and concife, in the practice of navigation, as 
Mr. Wright’s conftrudtion, efpecially in determining 
the bearings or courfes from place to place : nor will 
it (I prefume) admit of a zone containing both north 
and fouth latitude. 
Of thefe inconveniences Mr. Murdoch feems to 
be extremely well acquainted, when he expreffes 
himfelf in the following very candid and ingenuous 
terms, viz. “ As to Wright’s or Mercator’s nauti- 
<c cal chart, it does not here fall under our conlide- 
“ rat'on : it is perfect in its kind ; and will always 
“ be reckoned among the chief inventions of the 
“ laft 
