L £26 J 
Ir is performed on the principles of middle latitude failing, 
thus: 
% 
Hatr the fum of both latitudes taken from go? is the com- 
plement of the middle latitude 37° 20, and the lefler longitude 
fubtraéted from the greater leaves the difference of longitude 
3° 30, or 210 miles. 
Move -the center of the femicircle to the proper latitude 
departed from 50” so’ N. and the edge of the index to the com- 
plement of the middle latitude 37° 20’ on the femicircle, then 
move the box until the edge of the perpendicular interfects 
the termination of the difference of longitude 210 miles on 
the index, which point of interfeGtion will mark the departure 
128 on the perpendicular, then move the edge of the perpen- 
dicular to the proper latitude arrived at, 54° 30’, and the index 
until it cuts the departure 128 on the perpendicular, then will 
the perpendicular mark the diftance on the index 254,7%, miles, 
and the index will mark the courfe on the femicircle 30° 10, 
or N. N. E. 3 E. nearly. 
G (A 5,7 EB; 5-H. 
Boru latitudes and courfe given, to find the diftance and dif 
ference of longitude. 
Lat. 50° 50 N. Long. 19° 00’ W. failed from, 
Lat. 54° 30 N. arrived at; courfe N. 30° 10 E. 
By 
