_A._ But then how are great drops frozen into hailstones, and that especially (as we see they are) in summer? _B._ It is especially in summer, and hot weather, that the drops of water which make the clouds, are great enough; but it is then also that clouds are sooner and more plentifully carried up. And therefore the current of the air strengthened between the earth and the clouds, becomes more swift; and thereby freezeth the drops of water, not in the cloud itself, but as they are falling. Nor does it freeze them thoroughly, the time of their falling not permitting it, but gives them only a thin coat of ice; as is manifest by their sudden dissolving. _A._ Why are not sometimes also whole clouds when pregnant and ready to drop, frozen into one piece of ice? _B._ I believe they are so whensoever it thunders. _A._ But upon what ground do you believe it? _B._ From the manner or kind of noise they make, namely a crack; which I see not how it can possibly be made by water or any other soft bodies whatsoever. _A._ Yes, the powder they call _aurum fulminans_, when thoroughly warm, gives just such another crack as thunder. _B._ But why may not every small grain of that _aurum fulminans_ by itself be heard, though a heap of them together be soft, as is any heap of sand. Salts of all sorts are of the nature of ice. But gold is dissolved into _aurum fulminans_ by nitre and other salts. And the least grain of it gives a little crack in the fire by itself. And therefore when they are so warmed by degrees, the crack cannot choose but be very great. _A._ But before it be _aurum fulminans_ they use to wash away the salt (which they call dulcifying it), and then they dry it gently by degrees. _B._ That is, they exhale the pure water that is left in the powder, and leave the salt behind to harden with drying. Other powder made of salts without any gold in them will give a crack as great as _aurum fulminans_. A very great chemist of our times hath written, that salt of tartar, saltpetre, and a little brimstone ground together into a powder, and dried, a few grains of that powder will be made by the fire to give as great a clap as a musket. _A._ Methinks it were worth your trial to see what effect a quart or a pint of _aurum fulminans_ would produce, being put into a great gun made strong enough on purpose, and the breech of the gun set in hot cinders, so as to heat by degrees, till the powder fly. _B._ I pray you try it yourself; I cannot spare so much money. _A._ What is it that breaketh the clouds when they are frozen? _B._ In very hot weather the sun raiseth from the sea and all moist places abundance of water, and to a great height. And whilst this water hangs over us in clouds, or is again descending, it raiseth other clouds, and it happens very often that they press the air between them, and squeeze it through the clouds themselves very violently; which as it passes shaves and hardens them in the manner declared.