Page:First Voyage Round the World.djvu/253

 line, at any hour of the day or night, looking at the moon or any star; and for these, place in the middle of the astrolabe instead of the verghezita or sight, two straight bars between which you will observe the star."

Thus the method being known by which the required direction is given to the ship, the author teaches the method for determining the point or degree on the chart of the winds, to which the ship on leaving a place to go to a given country should be directed. For clearness, he gives some examples of this. "Do you wish," he says, "to go from south to north, or vice versâ, on the same longitude? always proceed on the same meridian. Do you wish to go from east to west, or vice versâ, in the same latitude? always proceed on the same parallel. Do you wish to go from one place to another as many degrees distant in longitude as it is different in latitude? Then take the course of 45 degrees either to the south-west or south-east, or north-west or north-east. If the latitude is greater than the longitude, then add to the 45 degrees as many degrees towards the nearest pole, as the number of degrees by which the latitude exceeds the longitude. For instance, if I wish to go from Cape St. Vincent to Cape Bojador, I reckon the degrees of longitude and those of latitude to know the difference between these two capes. I find that the degrees of longitude are five and a half, and those of latitude are eleven, from which I subtract the degrees of longitude and there remain 5 deg. 30 min. Then, instead of going in the direction of from north-east to south-west (as I should do if the longitude were equal to the latitude], I go from 5 deg. 30 min. above north-east towards north, to 5 deg. 30 min. below south-west towards south. If the longitude is greater than the latitude, the lesser number is still subtracted from the greater: and the direction will be 45 deg. after deducting the residue.