Q. Why does the escape of air from the chestnut, or the explosion of gunpowder, produce a report?
A. Because a quantity of air (suddenly let loose) pushes against the air around, in order to make room for itself; and as the air of the chestnut slaps against the air of the room, a report is made, (as when I slap a book or table).
Q. If a chestnut be slit, it will not crack; why is this?
A. Because the heated air of the chestnut can freely escape through the slit in the rind.
Q. Why does an apple spit and spurt about, when roasted?
A. An apple contains a vast quantity of air, which (being expanded by the heat of the fire) bursts through the peel, carrying the juice of the apple along with it.
Q. Does an apple contain more air, in proportion, than a chestnut?
A. Yes, much more. There is as much condensed air in a common apple, as would fill a space 48 times as big as the apple itself.