_A._ That has already been granted; my question is what breaks them? _B._ I must here take in one supposition more. _A._ Then your basin, it seems, holds not all you have need of. _B._ It may for all this, for the supposition I add is no more but this; that what internal motion I ascribe to the earth, and the other concrete parts of the world, is to be supposed also in every of their parts how small soever; for what reason is there to think, in case the whole earth have in truth the motion I have ascribed to it, that one part of it taken away, the remaining part should lose that motion. If you break a loadstone, both parts will retain their virtue, though weakened according to the diminution of their quantity; I suppose therefore in every small part of the earth the same kind of motion, which I have supposed in the whole: and so I recede not yet from my basin. _A._ Let it be supposed, and withal, that abundance of earth, (which I see you aim at), be drawn up together with the water. What then? _B._ Then if many pregnant clouds, some ascending and some descending meet together, and make concavities between, and by the pressing out of the air, as I have said before, become ice; those atoms, as I may call them, of earth will, by the straining of the air through the water of the clouds, be left behind, and remain in the cavities of the clouds, and be more in number than for the proportion of the air therein. Therefore for want of liberty they must needs justle one another, and become, as they are more and more straightened of room, more and more swift, and consequently at last break the ice suddenly and violently, now in one place, and by and by in another; and make thereby so many claps of thunder, and so many flashes of lightning. For the air recoiling upon our eyes, is that which maketh those flashes to our fancy. _A._ But I have seen lightning in a very clear evening, when there has been neither thunder nor clouds. _B._ Yes, in a clear evening; because the clouds and the rain were below the horizon, perhaps forty or fifty miles off; so that you could not see the clouds nor hear the thunder. _A._ If the clouds be indeed frozen into ice, I shall not wonder if they be sometimes also so situated, as, like looking-glasses, to make us see sometimes three or more suns by refraction and reflection. ========== CHAPTER VII. PROBLEMS OF MOTION PERPENDICULAR, AND OBLIQUE; OF PRESSION AND PERCUSSION; REFLECTION AND REFRACTION; ATTRACTION AND REPULSION.