My silence as to Africa,[423] Spain, and the provinces of Gaul, will occasion no surprise, from the fact that no one has published any observations made upon the stars in those countries. Still, however, there will be no difficulty in calculating them, even for these regions as well, on reference being made to the parallels which have been set forth in the Sixth Book.[424] By adopting this course, an accurate acquaintance may be made with the astronomical relations, not only of individual nations, but of cities even as well. By taking the circular parallels which we have there appended to the several portions of the earth respectively, and applying them to the countries in question, that are similarly situate, it will be found that the rising of the heavenly bodies will be the same for all parts within those parallels, where the shadows projected are of equal length. It is also deserving of remark, that the seasons have their periodical recurrences, without any marked difference, every four years, in consequence of the influence[425] of the sun, and that the characteristics of the seasons are developed in excess every eighth year, at the revolution of every hundredth moon. CHAP. 58.—THE RISING AND SETTING OF THE STARS. The whole of this system is based upon the observation of three branches of the heavenly phænomena, the rising of the constellations, their setting, and the regular recurrence of the seasons. These risings and settings may be observed in two different ways:—The stars are either concealed, and cease to be seen at the rising of the sun, or else present themselves to our view at his setting—this last being more generally known by the name of “emersion” than of “rising,” while their disappearance is rather an “occultation” than a “setting.”—Considered, again, in another point of view, when upon certain days they begin to appear or disappear, at the setting or the rising of the sun, as the case may be, these are called their morning or their evening settings or risings, according as each of these phænomena takes place at day-break or twilight. It requires an interval of three quarters of an hour at least before the rising of the sun or after his setting, for the stars to be visible to us. In addition to this, there are certain stars which rise and set twice.[426] All that we here state bears reference, it must be remembered, to the fixed stars only. CHAP. 59.—THE EPOCHS OF THE SEASONS.