I had a very nice letter a week or two ago from a Wicklow man who has an inflatable globe above his bed. Every morning he opens his eyes to a view of the southern hemisphere, and as the globe slowly rotates upon its thread, the Trans-American Airlines Super Constellation aircraft suspended adjacent to it from the ceiling appears to circumnavigate this beach-ball world.
And this, he says, very often makes him wonder. He wonders why, by convention, he is constrained each morning to view Antarctica, the southern tips of South America and Africa, and the Great Australian Bight. Why, in other words, is a globe always mounted with the north pole uppermost, and why, in the case of two-dimensional representation of the surface of the Earth, is north always at the top?
It all goes back to an Egyptian called Claudius Ptolemaeus, whom we know better by the name of Ptolemy. He was born about AD 85, and he summarised the cartographical knowledge of the day in his treatise Geographia. His definitive map of the known world, which stretched from Iceland and the Canary Islands in the east, to Ceylon in the west, shows remarkable agreement with the familiar patterns we know today. The little island of Hibernia was just apparent at the north-west corner.
Understandably enough, Ptolemy's map is centred on Alexandria, but most importantly, north was at the top; it was orientated in the direction of the North Star, recognising the fact that Polaris was the constant guiding light for voyagers at the time.
During the Middle Ages, however, religious influences came to be predominant, and mapmakers were constrained by what the Bible had to say on cartographic matters. It was noticed, for example, that there was reference in Isaiah, chapter 12, to "the four corners of the earth" which obviously meant that the world was rectangular rather than spherical; many contemporary maps reflected this interpretation. Alternatively, one could follow Ezekiel, chapter five, which declared that "God hath set Jerusalem in the midst of the nations and countries of the world", so pious map-makers drew the world as a wheel with the holy city at the hub; as a consequence, on local maps, east was always at the top.
In the 14th century, however, cartography escaped from stagnation and regression. With the spread of maritime trade and exploration, and increasing reliance on magnetic compasses, more accurate maps began to appear. North once again assumed its place at the top of the page, so that features on the map could be readily aligned with true and magnetic north.