Gnomon
Sundial
Pytheas also made other astronomical measurements which show him to have been a remarkably good observer. He found that the pole of the heavens did not coincide, as the earlier astronomer Eudoxus had supposed, with any star; but that it made an almost regular rectangle with three stars lying near it.[40] The pole of the heavens was naturally of consequence to Pytheas, who steered by the stars; but it is nevertheless striking that he should have considered it necessary to measure it with such accuracy, if he had not some other object in doing so. He may have required the pole for the adjustment of the equinoctial sun-dial (“polus”), whose pointers had to be parallel with the axis of the heavens;[41] but it is also possible that he had discovered that by measuring the altitude of the pole above the horizon he obtained directly the latitude of the spot on the earth, and that this was a simpler method of determining the latitude than by measuring the altitude of the sun by a gnomon. Nor is it likely that he possessed the requisite knowledge for calculating gnomon measurements unless they were taken either at the solstice or the equinox. To judge by quotations in various authors he must have given the latitude of several places in numbers of parts of a circle north of Massalia.[42] These results of his may perhaps be partly based on measurements of the polar altitude. Whether Pytheas was acquainted with any instrument for the measurement of angles we do not know; but it is not unlikely, since even the Chaldeans appear to have invented a kind of parallactic rule, which was improved upon by the Alexandrians, and was called by the Romans “triquetrum” (regula Ptolemaica). The instrument resembled a large pair of compasses with long straight rods for legs, and the angle was determined by measuring, in measure of length, the distance between these two legs.[43] As the pole of the heavens did not coincide with any star, such measurements cannot have been very accurate, unless Pytheas took the trouble to measure a circumpolar star in its upper and lower culmination; or, indeed, in only one of them, for he may easily have found the distance of the star from the pole by his earlier observations to determine the position of the pole itself. It is also quite possible that by the aid of the rectangle formed by the pole with three stars, he was able to obtain an approximate measurement of the altitude of the pole. Another indication used by the Greeks to obtain the latitude of a place was the length of its longest day. To determine this Pytheas may have used the equinoctial dial (“polus”), or the water-clock, the “clepsydra” of the Greeks.
Greek trading-vessel and longship (warship), from a vase painting (about 500 B.C.)
Pytheas’s ship
It is not known what kind of ship he had for his voyage; but if it was equal to the best that Massalia at that time could afford, it may well have been a good sea-craft. As it was necessary to be prepared for hostilities on the part of the Carthaginians and Gaditanians, he doubtless had a warship (longship), which sailed faster than the broader merchantmen, and which could also be rowed by one or more banks of oars. It may have been considerably over 100 feet long, and far larger than those in which later the Norsemen crossed the Atlantic. It has been asserted that Pytheas must have gone on foot for the greater part of his journey, since, according to Strabo [ii. 104], he is said to have stated “not only that he had visited the whole of Britain on foot, but he also gives its circumference as more than 40,000 stadia.” But, as Professor Alf Torp has pointed out to me, it is not stated that he “traversed” it, but “visited” it on foot. The meaning must be that he put in at many places on the coast, and made longer or shorter excursions into the country. That a man should be able to traverse such great distances alone on foot, through the roadless and forest-clad countries of that period, seems impossible.
