JOS DESCRIPTION OF GARNETT S 



difference of longitude to be 6° 0' required the latitude arrived 

 at, and the course the vessel has steered ? 



1st, Place the Index to the given latitude, and on the left 

 hand on 3 degrees, (the half of the given difference of longi- 

 tude) and extend the given distance 300 miles, to 3° differ- 

 ence of longitude on the right hand; then the latitude arrived at 

 will be found 53° 45' N. and the course N. 47° E. Q. E. I. 



CASE VII. 



Given the Course, Distance, and Difference of Longitude, to 

 find both Latitudes. 



RULE. 



Place the Index on any parallel of latitude to the required 

 course, and if the given distance subtend a less difference of 

 longitude that the given, (always making an equal difference 

 of longitude on both sides the central meridian) move it upwards 

 to a higher latitude, or if it subtend a greater difference of longi- 

 tude, move it downwards to a lower latitude until the distance 

 subtend the given difference of longitude, and the required 

 latitudes will be found. 



N. B. When the course is on the meridian, this case is in- 

 determinate, and the nearer to the meridian, the less accurate 

 will be the solution. 



CASE VIII. 



Given the Course, Difference of Latitude, and Difference of 

 Longitude, to find both Latitudes. 



This case is similar to case 7th. using the difference of lati- 

 tude instead of the distance, which is always known when the 

 course and difference of latitude are given. 



N. B. This CASE like the LAST is also indeterminate 

 when the course is on the meridian, and less accurate when 

 near it. 



