The first voyage round the world, by Magellan

by Antonio Pigafetta

The armillary sphere, of which the author gives a drawing, serves to explain the system of the world according to Ptolemy, and could also serve as an astrolabe, for one sees at the top of it a kind of handle or ring, by which to hold it suspended, as is seen in the above-mentioned drawing. He begins his treatise by giving us an idea of that system, as have done all those after him, who have written of the elements of the nautical art and of pilotage.

“The earth is round,” he says, “and remains suspended and immovable in the midst of all the celestial bodies. The first index fixed on two poles, the arctic and antarctic, which are supposed to correspond with the poles of the earth. It runs from East to West, and transports with itself all the planets and stars. Besides this there is the eighth sphere, the poles of which are at 23 deg. 33 min.,⁠[419] it runs from West to East.”

“It is supposed that all the circumference of the earth is divided into 360 degrees; and each degree is of 17 leagues and a half, consequently the circumference of the earth is 6,300 leagues. Land leagues are of three miles and sea leagues of four miles.⁠[420]”

“The ten circles of the armillary sphere, of which the six major pass through the center of the earth, serve to determine the situation of countries and climates. The Ecliptic determines the movement of the sun and the planets: the two Tropics indicate the point to which the sun declines from the equator towards the North in summer, and towards the South in winter. The Meridian, always variable, because it passes through all points of the equator, cutting it perpendicularly, designates the longitude, and it is on it that the latitudes are marked.”

Of Latitude.

After having well explained the armillary sphere with all its parts, and their use according to the system of Ptolemy, the author goes on to teach the method of taking the altitude of the pole, on which the latitude is calculated; fixing the pole at 0° and the equator at 90°.

“The Polar star,” he says, “is not precisely on the point corresponding to the axis of the earth; but it turns round it, as do all the other stars. In order to know its true position with regard to the pole, it must be observed where the Guard stars⁠[421] stand. If these are on the western arm,⁠[422] the polar star stands one degree above the pole: if they are on the line⁠[423] the pole star stands 3 deg. 30 min.⁠[424] below the pole: if they are on the eastern arm the pole star is one degree below the pole. When one wishes to take the altitude of the pole star, in whichever of the above-mentioned four places the Guard stars may be, the degrees which the pole star has above the pole will be subtracted from its altitude, or those which it has below the pole will be added to it. I have spoken in the account of the voyage of the stars of the Antarctic Pole.”

“The latitude of the place may also be ascertained by the sun’s altitude. 1. If you find yourself between the equinoctial and the arctic pole and the shadow falls towards that pole, look how many degrees and minutes meridianal declination the sun has that day; and this you will subtract from the altitude of the sun which you have taken: afterwards, deducting the remaining degrees from 90 deg., you will have in the residue the number of degrees of North latitude, that is your distance from the equator. 2. If the sun has a boreal declination, in such a manner that the shadow falls towards the south, take the sun’s declination on that day, and add it to the sun’s altitude which you have taken, from that sum subtract 90 degs., and the remaining degrees will indicate your boreal latitude. 3. If the sun is between the equinoctial and the antarctic, and the shadow falls towards the antarctic, observe the sun’s declination for that day, subtract it from the altitude taken, according to the first rule, and you will have the degrees of south latitude. 4. If, when you and the sun are between the equinoctial and the antarctic pole, the shadow falls towards the north, you will add the altitude you have taken to the sun’s declination that day, and act according to the second rule. 5. When you have an altitude of 90 deg., you will be so many degrees distant from the equator as there are degrees of the sun’s declination, and if the sun has no declination you will be under the equator. 6. If you are to the north of the equator, and the sun is in the southern signs you will look what is its declination, you will add these degrees of declination to those of the altitude observed, and as many degrees as are wanting from 90 deg., so many will you be distant from the equinoctial. 7. You will do the same when you find yourself to the south of the equinoctial, whilst the sun is in the northern signs.”

Of Longitude.

“Longitude indicates the degrees from east to west: I have considered many methods or means for ascertaining it, and I have found three methods⁠[425] fitting for that object. The last is the most convenient for those who do not know astrology. At the present time the pilots content themselves with knowing the latitude; and are so proud that they will not hear speak of longitude.”