By. Mercator’s failing. 
e 
Move the box and femicircle as in the former cafe to the 
meridional parts of the given latitudes, then fet the index to the 
courfe, and it will mark the difference of longitude 3° 30° on 
the perpendicular 15° 30 W... 
Tuen to find the diftance move the perpendicular and femi- 
circle to the proper latitudes given, and the perpendicular will: 
cut the diftance'2§42; miles on the index.. 
By middle Latitude failing. 
Complement of the middle Lat. 37° 20% 
Move the femicircle and perpendicular to the latitudes given. 
and the index to the courfe, then the perpendicular will fhow the 
departure 128 miles, and the index the diftance 254%, miles, at- 
the point of interfection. 
To find the difference of longitude fet the index to the 
- complement of the middle latitude on the femicircle, and move: 
the box until the termination of the departure on the perpendi-- 
cular meets the index, which will mark the difference of longi- 
‘tude thereon 210 miles, or 3° 30. 
GASE 
