_A._ Yes; I remember you told me before, that upon any strong pressure of the eye, the resistance from within would appear a light. But to return to the enquiry of heat and cold, there be two things that beyond all other put me into admiration. One is the swiftness of kindling in gunpowder. The other is the freezing of water in a vessel, though not far from the fire, set about with other water with ice and snow in it. When paper or flax is flaming, the flame creeps gently on; and if a house full of paper were to be burnt with putting a candle to it, it will be long in burning; whereas a spark of fire would set on flame a mountain of gunpowder in almost an instant. _B._ Know you not gunpowder is made of the powder of charcoal, brimstone, and saltpetre? Whereof the first will kindle with a spark, the second flame as soon as touched with fire; and the third blows it, as being composed of many orbs of salt filled with air, and as it dissolveth in the flame, furiously blowing increaseth it. And as for making ice by the fireside; it is manifest that whilst the snow is dissolving in the external vessel, the air must in the like manner break forth, and shave the superficies of the inner vessel, and work through the water till it be frozen. _A._ I could easily assent to this, if I could conceive how the air that shaves, as you say, the outside of the vessel, could work through it. I conceive well enough a pail of water with ice or snow dissolving in it, and how it causeth wind. But how that wind should communicate itself through the vessel of wood or metal, so as to make it shave the superficies of the water which is within it, I do not so well understand. _B._ I do not say the inner superficies of the vessel shaves the water within it. But it is manifest that the wind made in the pail of water by the melting snow or ice presseth the sides of the vessel that standeth in it; and that the pressure worketh clean through, how hard soever the vessel be; and that again worketh on the water within, by restitution of its parts, and so hardeneth the water by degrees. _A._ I understand you now. The ice in the pail by its dissolution transfers its hardness to the water within. _B._ You are merry. But supposing, as I do, that the ice in the pail is more than the water in the vessel, you will find no absurdity in the argument. Besides, the experiment, you know, is common.