_A._ But has that endeavour no effect at all before the impediment be removed? For if endeavour be motion, and every motion have some effect more or less, methinks this endeavour should in time produce something. _B._ So it does. For in time (in a long time) the course of this internal motion will lie along the bow, not according to the former, but to the new acquired posture. And then it well be as uneasy to return it to its former posture, as it was before to bend it. _A._ That is true. For bows long bent lose their appetite to restitution, long custom becoming nature. But from this internal reciprocation of the parts, how do you infer the hardness of the whole body? _B._ If you apply force to any single part of such a body, you must needs disorder the motion of the next parts to it before it yield, and there disordered, the motion of the next again must also be disordered; and consequently no one part can yield without force sufficient to disorder all: but then the whole body must also yield. Now when a body is of such a nature as no single part can be removed without removing the whole, men say that body is hard. _A._ Why does the fire melt divers hard bodies, and yet not all? _B._ The hardest bodies are those wherein the motion of the parts are the most swift, and yet in the least circles. Wherefore if the fire, the motion of whose parts are swift, and in greater circles, be made so swift, as to be strong enough to master the motion of the parts of the hard body, it will make those parts to move in a greater compass, and thereby weaken their resistance, that is to say, soften them, which is a degree of liquefaction. And when the motion is so weakened, as that the parts lose their coherence by the force of their own weight, then we count the body melted. _A._ Why are the hardest things the most brittle, insomuch that what force soever is enough to bend them, is enough also to break them? _B._ In bending a hard body, as (for example) a rod of iron, you do not enlarge the space of the internal motion of the parts of iron, as the fire does; but you master and interrupt the motion, and that chiefly in one place. In which place the motion that makes the iron hard being once overcome, the prosecution of that bending must needs suddenly master the motions of the parts next unto it, being almost mastered before. _A._ I have seen a small piece of glass, the figure whereof is this, A A B C. Which piece of glass if you bend toward the top, as in C, the whole body will shatter asunder into a million of pieces, and be like to so much dust. I would fain see you give a probable reason of that.