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 For instance, do you want to go from the island of Ferro to Guadeloupe; you know that the first is in 27 deg. latitude and the second in 15 deg.; then take their difference, which is 12 deg.: look at the map for their longitude, and you see that Ferro is in 1 deg. and Guadeloupe in 45 deg., whence their difference is 44 deg.: subtract from these the 12 deg. residue of latitude, and there remain 32 deg. Then you must subtract these 32 deg. from 45 deg., and there will remain 13 deg. Therefore your course will be from north-east 13 deg. north to south-west 13 deg. south.

"The rose of the winds, divided into 360 deg., will give a clearer idea of what has been here said; it being well understood that the pilot must place the center of the winds on the point from which he starts, or from which he takes the course, and he must fix the pole to the true pole observed from the sun, and not trusting to the compass, which north-easts or north-wests.

"Then, to ascertain whence comes the wind, place a little stick with a little sail in the centre of your rose or circle of winds, divided into 360 deg., and placed in such a manner that north and south stand on the true Solar meridian. The direction of the vane moved by the wind will indicate exactly which wind blows: on the equinoctial is east and west; at 45 deg. there is north-east, south-west, north-west, and south-east; at 22½ deg. towards north you have north-north-east, and so on with the others."