The annual risings of stars had formerly, in the absence of more accurate means of observation, an importance they no longer possess. Mariners and husbandmen, accustomed to watch, because at the mercy of the heavens, could hardly fail no less to be struck with the successive effacements by, and re-emergences from, the solar beams, of certain well-known stars, as the sun pursued his yearly course amongst them, than to note the epochs of such events. Four stages in these periodical fluctuations of visibility were especially marked by primitive observers. The first perceptible appearance of a star in the dawn was known as its ‘heliacal rising.’ This brief glimpse extended gradually as the star increased its seeming distance from the sun, the interval of precedence in rising lengthening by nearly four minutes each morning. At the end of close upon six months occurred its ‘acronycal rising,’ or last visible ascent from the eastern horizon after sunset. Its conspicuousness was then at the maximum, the whole of the dark hours being available for its shining. To these two epochs of rising succeeded and corresponded two epochs of setting—the ‘cosmical’ and the ‘heliacal.’ A star set cosmically when, for the first time each year, it reached the horizon long enough before break of day to be still distinguishable; it set heliacally on the last evening when its rays still detached themselves from the background of illuminated western sky, before getting finally immersed in twilight. The round began again when the star had arrived sufficiently far on the other side of the sun to show in the morning—in other words, to rise heliacally. Wide plains and clear skies gave opportunities for closely and continually observing these successive moments in the revolving relations of sun and stars, which were soon found to afford a very accurate index to the changes of the seasons. By them, for the most part, Hesiod’s prescriptions for navigation and agriculture are timed; and although Homer, in conformity with the nature of his subject, is less precise, he was still fully aware of the association.