certain places at certain intervals in the heavens, if circumstances are favourable ; or because at times the heaven lias a pa rticular motion above us so that such stars appear ; or because the stars themselves a re set in motion under certain conditions and come to our neighbourhood and show themselves. And their disappearance is due to the causes which are the opposite of these. Certain stars may revolve without settings not only for the reason alleged by some, because this is the part of the world round which, itself unmoved, the rest revolves, but it may also be because a circular eddy of air surrounds this part, which prevents them from travelling out of sight like other stars ; or because there is a dearth of necessary fuel farther on, while there is abundance in that part where they are seen to be. Moreover there are several other ways in which this might be brought about, as may be seen by anyone capable of reasoning in accordance with the facts. The wanderings ojLcertain stars, if such wandering is their actual motion, and the regular movement of certain other stars, may be accounted for by saying that they originally moved in a circle and were constrained, some of them to be whirled round with the same uniform rotation and others with a whirling motion which varied ; but it may also be that according to the diversity of the regions traversed in some places there are uniform tracts of air, forcing them forward in one direction and burning uniformly, in others these tracts present such irregularities as cause the motions observed. To assign a single cause for these effects when the facts suggest several causes is madness and a strange inconsistency ; yet it is done by adherents of rash astronomy, who assign meaning-