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Bora latitudes and diftance given, to find the courfe and dif- 
ference of longitude, 
Lat. 50° 50’ N. Long. 19° 00 W. failed from, 
Lat. 54° 30 N, arrived at, diftance-failed 254-7, miiles. 
Move the perpendicular and femicircle to'the proper latitudes 
given, and the index until the diftance. failed marked om it 
meets the perpendicular, then the index will mark the courfe 
N. 30° 10’ E. on the femicircle, 
To find the difference of longitude, ferew faft the index to 
this courfe, move perpendicular and femicircle to the meridional 
parts of the given latitudes, and the {pace intercepted between 
the limb of the box and the index will fhow the difference of 
longitude 3° 30. 
By middle Latitude failing. 
\ 
Complement of middle Lat. 37° 20. 
Move the femicircle and perpendicular to the given latitudes, 
and the index until the diftance failed marked on it cuts the per- 
pendicular, then the‘ perpendicular will fhow the departure 128 
miles, and the femicircle the courfe N. 30° 10 E. 
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