[Sidenote: Astronomical measurements in Britain]
From statements of Hipparchus, preserved by Strabo [ii. 71, 74, 75, 115, 125, 134], we may conclude that Pytheas obtained astronomical data at various spots in Britain and Orkan. Hipparchus has made use of these in his tables of climate, and he was able from them to point out that the longest day in the most northern part of Britain was of eighteen equinoctial hours,[48] and in an inhabited country, which according to Pytheas lay farther north than Britain, the longest day was of nineteen equinoctial hours. If the length of day is fixed in round numbers of hours, a longest day of eighteen hours fits the northernmost part of Scotland,[49] while the country still farther north with a longest day of nineteen hours agrees exactly with Shetland.[50] These data are important, as they show that Pytheas must have been in the most northerly parts of the British Isles, and reached Shetland.[51]
But the bold and hardy explorer does not seem to have stopped here. He continued his course northward over the ocean, and came to the uttermost region, "Thule," which was the land of the midnight sun, "where the tropic coincides with the Arctic Circle."[52]
On this section of Pytheas's voyage Geminus of Rhodes (1st century B.C.) has an important quotation in his Astronomy [vi. 9]. After mentioning that the days get longer the farther north one goes, he continues:
To these regions [i.e., to the north] the Massalian Pytheas seems also to have come. He says at least in his treatise "On the Ocean": "the Barbarians showed us the place where the sun goes to rest. For it was the case that in these parts the nights were very short, in some places two, in others three hours long, so that the sun rose again a short time after it had set."
The name of Thule is not mentioned, but that must be the country in question. It does not appear from this whether Pytheas himself thought that the shortest night of the year was of two or three hours, or whether that was the length of the night at the time he happened to be at these places; but the first case is doubtless the more probable. At any rate Geminus seems to have understood him thus, since in the passage immediately preceding he is speaking of the regions where the longest day is of seventeen or eighteen hours, and he goes on to speak of those where the longest day is of twenty-three hours. If on the other hand it is the length of the night at the time Pytheas was there that is meant, then it seems strange that he should require to be shown by the barbarians where the sun rose and set, which he could just as well have seen for himself; for it is scarcely credible that after having journeyed so far his stay should have been so brief that the sky was overcast the whole time.[53]