Q. Why is our breath visible in winter-time?
A. Because it is condensed by the cold air into small drops, which are visible to the eye.
Q. Why do steam-engines sometimes burst?
A. Steam is very elastic; and this elasticity increases in a greater proportion than the heat which produces it; unless, therefore, some vent be freely allowed, the steam heaves and swells, till it bursts the vessel which confined it.
Q. What becomes of the steam, after it has been condensed?
A. It is dissolved by the air, and forms a part of its invisible vapour.
Q. Is air a good conductor?
A. No; air is a very bad conductor, and is heated (like water) by convection.
Q. How is a room warmed by a stove?