We have thus the following observations, that might be made with respect to this, or any other well-marked constellation. First, the period during which it was visible at sunset; secondly, the date of its culmination at midnight; thirdly, its setting in the evening; and fourthly, its rising in the morning: the last two dates being nearly six months removed from the second. There are also the dates of its culmination at sunrise and sunset, which would divide these intervals into two equal halves. On account of the precession of the equinoxes, as explained in the last chapter, the time at which the sun has any particular position with respect to the stars, grows later year by year in relation to the equinoctial points. And as we regulate our year by the date of the sun's entrance on the northern hemisphere, the sidereal dates, as we may call them, keep advancing on the months. As, however, the change is slow, it has not prevented years being commenced and husbandry being regulated by the dates above mentioned. Any date that is regulated by the stars we might expect to be nearly the same all over the world, and the customs observed to be universal, though the date itself might alter, and in this way. So long as the date was directly obtained from the position of the star, all would agree; but as soon as a solar calendar was arranged, and it was found that at that time this position coincided with a certain day, say the Pleiades culminating at midnight on November 17, then some would keep on the date November 17 as the important day, even when the Pleiades no longer culminated at midnight then, and others would keep reckoning by the stars, and so have a different date. With these explanations we shall be able to recognise how much the configurations of the Pleiades have had to do with the festivals and calendars of nations, and have even left their traces on customs and names in use among ourselves to the present day.