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twenty-four hours,—in other words, the interval be-tween successive risings will be yet further lengthenedthan we have found it to be on the assumption thatthe moon moved in the ecliptic. On the contrary, ifthe moon, when crossing the ecliptic ascendingly, isat her descending node (so following the course E 2),while when crossing the ecliptic descendingly she isat her ascending node (so following the course E 3),the intervals between successive risings and settingswill be less markedly affected than on the assumptionthat the moon moves in the ecliptic. These are theextreme cases either way. It is readily seen, how-ever, that the position of the moon as to the perigeeand apogee of her orbit must also have an effect,since her motion from E will be greater or lessaccording as she is nearer or farther from her perigee,and the interval between successive risings will bediminished or increased respectively.
Taking all these considerations into account, it isfound that instead of the moon risings about 20minutes later night after night for several successivedays at the time of harvest moon, she at times rises onlynine or ten minutes later on successive nights ; whileat other times, at the same season, the differenceexceeds half an hour. As regards the maximum dif-ference between the hours of rising of the full moonin spring, it varies from about an hour and tenminutes to about an hour and a half.
It is to be noticed that in every lunation corre-sponding variations occur, because the moon neces-