Q. Why will the wheelwright’s hoop fit the nave more easily, because they are made red-hot?
A. As iron expands by heat, the hoops will be larger when they are hot; and (being larger) will go on the nave more easily.
Q. Why will the hoops, which have been put on hot, girt the nave more firmly?
A. As iron contracts by cold, the hoops will shrink as they cool down; and, therefore, girt the nave with a tighter grasp.
Q. Why does a farrier put the horse-shoe on hot?
A. That it may stick the closer, when it has contracted by cold.
Q. Why does a stove make a cracking noise, when a fire is very hot?
A. The iron stove expands by heat, and (as it swells) the parts rub both against each other, and against the bricks around, driving them further off; and this produces a cracking noise.
Q. Why does a stove make a similar cracking noise, when a large fire is taken down?