_B._ The motion I have hitherto supposed but in the earth, I suppose also in the moon, and in all those great bodies that hang in the air constantly, I mean the stars, both fixed and errant. And for the sun and moon, I suppose the poles of their motion to be the poles of the equinoxial. Which supposed, it will follow (because the sun, the earth, and the moon, at every full and change are almost in one straight line) that this motion of the earth will then be made swifter than in the quarters. For this motion of the sun and moon being communicated to the earth, that hath already the like motion, maketh the same greater; and much greater when they are all three in one straight line, which is only at the full and change, whose tides are therefore called spring tides. _A._ But what then is the cause that the spring tides themselves are twice a-year, namely, when the sun is in the equinoxial, greater than at any other times? _B._ At other times of the year, the earth being out of the equinoxial, the motion thereof, by which the tides are made, will be less augmented, by so much as a motion in the obliquity of twenty-three degrees, or thereabout, which is the distance between the equinoxial and ecliptic circles, is weaker than the motion which is without obliquity. _A._ All this is reasonable enough, if it be possible that such motions as you suppose in these bodies, be really there. But that is a thing I have some reason to doubt of. For the throwing off of air, consequent to these motions, is the cause, you say, that other things come to the earth; and therefore the like motions in the sun and moon and stars, casting off the air, should also cause all other things to come to every one of them. From whence it will follow, that the sun, moon, and earth, and all other bodies but air, should presently come together into one heap. _B._ That does not follow. For if two bodies cast off the air, the motion of that air will be repressed both ways, and diverted into a course towards the poles on both sides; and then the two bodies cannot possibly come together. _A._ It is true. And besides, this driving of the air on both sides, north and south, makes the like motion of air there also. And this may answer the question, how a stone could fall to the earth under the poles of the ecliptic, by the only casting off of air? _B._ It follows from hence, that there is a certain and determinate distance of one of these bodies, the stars, from another, without any very sensible variation. _A._ All this is probable enough, if it be true that there is no vacuum, no place empty in all the world. And supposing this motion of the sun and moon to be in the plain of the equinoxial, methinks that this should be the cause of the diurnal motion of the earth; and because this motion of the earth is, you say, in the plain of the equinoxial, the same should cause also a motion in the moon on her own centre, answerable to the diurnal motion of the earth.