The obliquity of the ecliptic was found to be 23° 51′ 15″, which was deducted from the altitude. The complement of the result was the latitude of the place less the semi-diameter of the sun. With the semi-diameter added, the result is almost exactly the latitude of the Marseilles observatory, 43° 18′ N. Such accuracy is remarkable. The next step taken by Pytheas was to fix upon the nearest star to the pole as a guide for steering the ship. He found that there was no star on the pole, but that there were two very close to it. These would have been, in those days, β Ursæ Minoris and α Draconis, and Pytheas used one of these as his pole-star. During the voyage the latitudes were obtained by observation of the longest days. This involved long detentions at some of the ports. The nearest approximation we can get to the date of the voyage of Pytheas is the time of Alexander the Great and of Aristotle, about 330 B.C.[8] A Grecian ship in those days was strongly built on regular principles, with sails on the mainmast, and rowing power. A large vessel would be 150 to 170 feet long, with a tonnage of 400 to 500, much larger and more seaworthy than the crazy little _Santa Maria_ in which, 1800 years afterwards, Columbus discovered the New World. Well provided with all the knowledge of his time, Pytheas weighed anchor and began his coasting voyage by the Pillars of Hercules and the Sacred Promontory, the western limit of the known world. The Greek ships of the time averaged about 50 miles a day. Sailing on along the coast, Oestrymnis (Cape Finistère) was reached, the probable farthest point of Himilco the Carthaginian. The island of Uxisama (Ushant) is mentioned, with an observation for the length of the longest day equal to 49° N. Thence a direct course was shaped for Cantion (Kent) where there was a long stay, and the island of Britain was thus discovered. Here Pytheas made a long journey into the interior, visiting Belerion (Cornwall) and the tin mines, and noting several details respecting the habits and customs of the people, our remote ancestors. In those days Britain was almost entirely in a wild state. The valleys were covered with primeval forests, their lower parts were occupied by vast swamps, and it was only on the downs and hill-ranges that there were _gwents_ or open clearings. Still, the people raised wheat and other cereals, had domestic animals, iron tools and arms, wooden chariots with iron fittings, and ornaments of bronze and gold. Pytheas must have traversed the great forest of Anderida on his way to the tin mines, and he found the people hospitable. They did not use open threshing-floors owing to the rains, but threshed their corn in large barns. They stored the corn in pits under ground, and made fermented liquor from barley, which they used as wine. Their houses were of wood and thatch, and Pytheas mentions the war chariots, but adds that the chiefs were generally at peace with each other.