## Note
The Longitude of one Place, and the Difference of Longitudes between that and another place, given to find the Longitude of that place.

### Rule
In East Longitude, Sailing to the Eastward, & in West Longitude, Sailing to the Westward, adding gives the Longitude of that East place if it exceeds not 18°; with the Name of that first place but if it does not exceed 100°, subtract it from 360°; if the remainder is the Longitude Required; of a Country name to that first in East Longitude. Sailing Westerly and in West Long. Sailing Easterly. Subtract gives the Long of the East Island whose name agrees with that in the Chart.

Sailing from Barbados, North Easterly till they differ of longitude be 32° 2' What Long is the ship in?

Long of Barbados 37° 5' 40"
Difference of Long 32° 2' 8"
Long: the Ship is in 5° 52' 48"

From the Lizard a Ship Sails South Westerly till her Difference of longitude be 32° 0' 20' what is the Ship's Longitude?

Lizard Longitude 2° 24' W
Difference of Long 32° 0' 2"
Long: the Ship is in 37° 26' W

Suppose a Ship Sails South Easterly from Bantam till her Difference of Long be 2000 Leagues her present Longitude is Required.

$$ \frac{20/2800}{24} = 100.66' $$

Bantam's Longitude 110°: 19' 6"
Diff: of Longitude 100°: 0' 8"
Sum 210°: 19'
Take from 360°: 360.00'
Rem. is her Longitude 149°: 41'

The Practical way of making and measuring Angles by the line of Chords &c.

1st OF THE CONSTRUCTION THERE

The lines of Chords is the Degree upon either or limb of the Quadrant of a Circle transferred into a Straight Line as in the Quadrant below, whereas the arch A & B D. is divided into 60 Degrees & these Degrees transferred to the Straight Line A G D, which is a Line of Chords and is known by placing one foot in and extending the other to the several Degrees on the limb of the Quadrant and so sweeping an arch till it Cut the line A G D, so that every Degree on the Line of Chords A G D. is the Same Distance from A as it is on the Limb or arch of the Quadrant D B & C: and therefore it is all one whether we measure any arch upon the Limb A & B D. or upon the lines of Chords D G A, E G G A, V O T E, the Chords of 60 Degrees (viz) A G, or A B, is always equal to 60°, or C A, V I A D I O N S C D. or C A.