_A._ I thought the greatest cold had been about the poles of the equator. _B._ And so did I once. But the reason commonly given for it is so improbable, that I do not think so now. For the cause they render of it is only, that the motion of the earth is swiftest in the equinoctial, and slowest about the poles; and consequently, since motion is the cause of heat, and cold is but, as it was thought, a want of the same, they inferred that the greatest cold must be about the poles of the equinoctial. Wherein they miscounted. For not every motion causeth heat, but this agitation only, which we call compounded motion; though some have alleged experience for that opinion; as that a bullet out of a gun will with its own swiftness melt. Which I never shall believe. _A._ It is a common thing with many philosophers to maintain their fancies with any rash report, and sometimes with a lie. But how is it possible that so soft a substance as water should be turned into so hard a substance as ice? _B._ When the air shaves the globe of the earth with such swiftness, as that of sixty miles in a minute of an hour, it cannot, where it meets with still water, but beat it up into small and undistinguishable bubbles, and involve itself in them as in so many bladders or skins of water. And ice is nothing else but the smallest imaginable parts of air and water mixed; which is made hard by this compounded motion, that keeps the parts so close together, as not to be separated in one place without disordering the motion of them all. For when a body will not easily yield to the impression of an external movent in one place without yielding in all, we call it hard; and when it does, we say it is soft. _A._ Why is not ice as well made in a moved as in a still water? Are there not great seas of ice in the northern parts of the earth?