_B._ Not the immediate cause. For the diurnal motion of the earth is upon its own centre, and therefore the sun’s motion cannot describe it. But it proceedeth as a necessary consequence from the annual motion. For which I have both experience and demonstration. The experiment is this: into a large hemisphere of wood, spherically concave, put in a globe of lead, and with your hands hold it fast by the brim, moving your hand circularly, but in a very small compass; you shall see the globe circulate about the concave vessel, just in the same manner as the earth doth every year in the air; and you shall see withal, that as it goes, it turns perpetually upon its own centre, and very swiftly. _A._ I have seen it: and it is used in some great kitchens to grind mustard. _B._ Is it so? Therefore take a hemisphere of gold, if you have it, the greater the better, and a bullet of gold, and, without mustard, you shall see the same effect. _A._ I doubt it not. But the cause of it is evident. For any spherical body being in motion upon the sides of a concave and hard sphere, is all the way turned upon its own centre by the resistance of the hard wood or metal. But the earth is a bullet without weight, and meeteth only with air, without any harder body in the way to resist it. _B._ Do you think the air makes no resistance, especially to so swift a motion as is the annual motion of the earth? If it do make any resistance, you cannot doubt but that it shall turn the earth circularly, and in a contrary way to its annual motion; that is to say, from east to west, because the annual motion is from west to east. _A._ I confess it. But what deduce you from these motions of the sun? _B._ I deduce, first, that the air must of necessity be moved both circularly about the body of the sun according to the ecliptic, and also every way directly from it. For the motion of the sun’s body is compounded of this circular motion upon the sphere L M, and of the straight motion of its semi-diameters from the centre A to the superficies of the sun’s body, which is L M. And therefore the air must needs be repelled every way, and also continually change place to fill up the places forsaken by other parts of the air, which else would be empty, there being no vacuum to retire unto. So that there would be a perpetual stream of air, and in a contrary way to the motion of the sun’s body, such as is the motion of water by the sides of a ship under sail. _A._ But this motion of the earth from west to east is only circular, such as is described by a compass about a centre; and cannot therefore repel the air as the sun does. And the disciples of Copernicus will have it to be the cause of the moon’s monthly motion about the earth.