This introduces another point which seems worth noticing. At present the ship Argo is never seen from any part of the earth's surface as pictured in fig. 39. When due south, the position whence in all northern latitudes the constellation is most favourably seen, the ship is always tilted up at the stern: one would say, in more nautical phrase, she is down by the head, if the ship had any fore-part; but from time immemorial she has been a half-ship only. Some 4,000 years ago, however, Argo stood nearly on an even keel when due south. Again, it is to the mighty gyrational motion of the earth that we have to look for the cause of the great change in the apparent position of the ship. The sphere of the fixed stars has remained all the time unchanged, or very nearly so, but the direction in which the earth's axis of rotation points has swayed round (much as the axis of a reeling top sways round) through about one-sixth part of a complete gyration. In the regions where astronomy first began as a science, Argo not only stood on an even keel but almost on the horizon when due south; and the features of resemblance to a ship, which I have endeavoured to portray in fig. 39, must have seemed much more striking there (and then) than now. The fore-part of the ship, or rather that region of the heavens where the fore-part should be, is occupied by great masses of the Milky Way in one of its brightest and most remarkable portions. I have sometimes fancied that in some of the old Zodiac temples of star-worshippers the constellation Argo was depicted as a mighty ship, gemmed with stars, and heavily laden in its fore-part with great masses of gilded cloud to represent the Milky Way, and that from such representations of the constellation came the tradition of the ship Argo and its cargo of golden fleece. Many parts of the story of Jason and his companions seem to relate to objects depicted in the old constellation-domes,--as those relating to the Dragon, to Hercules, Castor and Pollux, the Centaur, etc. There is also a curious reference, in the tradition, to the stern of the ship, which is much like what we can imagine as resulting from an attempt to explain the appearance of this part only, in the set of constellation figures. We read that the entrance to the Euxine Sea was fabled to be closed up by certain rocks called Symplegades (the Clashers), which floated on the water, and when anything attempted to pass through came together with such velocity that not even birds could escape. Phineas advised them to let a bird fly through, and if the bird passed safely, to venture the passage. It passed with only the loss of its tail; and the Argo, favoured by Juno, and impelled by the utmost efforts of its heroic crew, passed also, though so narrowly that the meeting rocks carried away part of her stern-works, which remained fixed there thenceforward.