If all young women had committed to memory these causes of evil and their remedies, many a badly-built chimney might have been cured, and many smoke-drawn tears, sighs, ill-tempers, and irritating words avoided. But there are dangers in this direction which demand special attention. Where one flue has two stoves or fireplaces, in rooms one above the other, in certain states of the atmosphere, the lower room, being the warmer, the colder air and carbonic acid in the room above will pass down into the lower room through the opening for the stove or the fireplace. This occurred not long since in a boarding-school, when the gas in a room above flowed into a lower one, and suffocated several to death. This room had no mode of ventilation, and several persons slept in it, and were thus stifled. Professor Brewer states a similar case in the family of a relative. An anthracite stove was used in the upper room; and on one still, close night, the gas from this stove descended through the flue and the opening into a room below, and stifled two persons to insensibility, though, by proper efforts, their lives were saved. Many such cases have occurred where rooms have been thus filled with poisonous gases, and servants and children destroyed, or their constitutions injured, simply because housekeepers are not properly instructed in this important branch of their profession. FURNACES. There is no improved mechanism in the economy of domestic life requiring more intelligent management than furnaces. Let us then consider some of the principles involved. The earth is heated by radiation from the sun. The air is not warmed by the passage of the sun's heat through it, but by convection from the earth, in the same way that it is warmed by the surfaces of stoves. The lower stratum of air is warmed by the earth and by objects which have been warmed by radiated heat from the sun. The particles of air thus heated expand, become lighter, and rise, being replaced by the descent of the cooler and heavier particles from above, which, on being warmed also rise, and give place to others. Owing to this process, the air is warmest nearest the earth, and grows cooler as height increases.