You keep bees. Here is a hive, I see, crowded with the busy insects. By the numbers that I observe clustering about the low arched door, and bustling out and in so incessantly, I learn that the industrious little fellows must be very closely packed together in their straw house. There must be many thousands of them dwelling together in a place that can not, at the most, equal more than a couple of square feet; and there is not a single window in the straw wall; no opening of any kind but the low, and half-choked entrance. Really, if those bees need to breathe, you who have furnished them with their dwelling must be nearly as bad as the cruel nabob, who shut up his prisoners in the Indian Black Hole!
Those bees certainly do need to breathe every bit as much as men and women; and what is more, they manage to breathe ten times better than you do at night. Notwithstanding all the crowding there is within their close dwelling, the air never gets there into the poisonous state in which the air of your sleeping room is by the morning. The bees take care that it shall not do so. Just bend down your ear and listen near the hive for a minute. Do you hear that incessant low humming? That is the bees hard at work, making an artificial wind. It is the sound of a couple of score of broad, stiff fans, flapping to and fro with great rapidity. Look, I drop this piece of light thistle-down near the door of the hive, and you see it is at once blown away from it by a steady draught. If you could see through the straw walls, you would notice twenty little sturdy fellows holding on to the floor of the hive with their feet, just within the door, and flapping their wings backwards and forwards without a moment’s pause. Now and then one or two tired insects drop out from the line of the fanners, but their places are immediately filled by fresh recruits, who lay hold of the floor and fall vigorously to work with their wings. This is the appointed band of air-purifiers, plying their business for the good of the entire community, and wafting a fresh breeze continuously through the hive. The bees take it by turns to carry on this necessary labor, and some of them are always at it. The humming caused by the rapid vibrations of their fans, scarcely ever ceases. It has been ascertained that air taken from the inside of a hive, is quite as pure as the fresh air that floats in the open space around; so perfectly do these little earnest workmen perform their purifying task.
The industrious bees, then, are an example to mankind. If people dwell in close rooms, they must cause an artificial breeze of fresh air to blow through them. Having shut out the great wind, that it may not chill too much by its uncontrollable currents, they must introduce such a little wind as they can keep thoroughly under control, but which nevertheless is sufficient to perform the office of purification as far as it is required. This process of causing an artificial wind to blow through the inside of a dwelling is called ventilation, from a Latin word which signifies “to blow” or fan with the wind.
In very hot climates where dwellings need to be ventilated for the sake of coolness, as well as for purification, men follow precisely the example set by the bees. They hang up broad and stiff canvas fans, which they call punkas, near the ceiling, and cause these to flap backwards and forwards constantly, by pulling them to and fro with ropes. In more temperate climates, it is rarely found necessary to take all this trouble, for the air readily makes currents of its own accord inside of rooms, if only allowed to do so. All that is necessary is the furnishing of a free passage into the room, and a free passage out, and it will then make a clear march through. One opening will not do, when fans are not kept going, because then the entering and departing air would meet face to face and obstruct each other. There must be “in” and “out” doors, just as one sees in much frequented offices and banks, in great towns.
A very effectual plan for securing the ventilation of a dwelling room consists in carrying a pipe of perforated zinc across the house, from outside wall to outside wall, just beneath the ceiling, allowing the ends to pass through the walls quite into the open air; then whichever end of the pipe chances to be most towards the quarter of the heavens from which the wind is blowing, should be closed with a plug, a free passage being left for the escape of the heated air through the opposite end. A number of holes should also be made through the door, near its bottom, until altogether they afford as much room to passing air as the inside bore of the zinc pipe. If you cannot manage to fix such a zinc pipe across the ceiling, why take out one or two of the panes of the window, and put into their place, plates of what is called perforated zinc (zinc plates pierced full of holes), such as you may buy for a trifle at any ironmongers. That is the next best thing you can do.
As soon as some arrangement of this kind has been completed, you will find that the air begins to move gently through the room, cold fresh air coming in through the holes in the door, and warm impure air being pressed out before it through the perforated zinc tubes or plates. This takes place partly because the external wind rushes, in its hasty way, against the openings through which the air is intended to enter, and forces itself in; but also, and more particularly, because the inside air gets warmer than the outside, and is then compelled to shift its quarters on that account.
The air contained inside of inhabited rooms gets warmed by the bodies and breaths of the persons living there. Then it is lighter, bulk for bulk, than the colder air outside, for warmth stretches and lightens everything. But as heavy things fall or press down to the earth more strongly than light ones, the cold air always squeezes into the room through the lower openings, and pushes the warm impure air out before it, through the upper ones.
When you light a fire in your room during cold weather, it makes a quick and strong draught through the room, for the same reason. Fires, indeed, are among the most powerful ventilators that can be brought into play. Let your fire out, and go on sitting in the room with two or three of your neighbors, and you will find the air of the room will be close and foul in half-an-hour, although it was quite fresh before. While the fire is burning, the chimney takes upon itself the office of the holes in the zinc tube or zinc plate fixed in the window, and the heated air of the room is pushed up through it by the fresh cold air which rushes in through all other openings and crevices. It is only in rooms where no fires are burning—as for instance, in your sleeping room—that holes through the walls and windows can serve as outlets for impure air.
But if you live with several companions, in small rooms, as some workpeople are compelled to do by their occupation, those rooms cannot get properly ventilated, even although fires are burning. Some of the poison-vapors, poured out from your living bodies with the breath, are so light that they are at once driven up to the top of the room, and collect there gradually, spreading lower and lower as they become more abundant. They can not get out through holes made in the walls or windows because, as we have seen, the fire causes streams of cold air to press in there.
A plan has been contrived, however, to ensure perfect ventilation even in small and crowded rooms, provided fires be burning. This plan consists in making an opening into the inside of the chimney, near to the ceiling, and fixing a balanced valve in it in such a way that the valve-plate is opened by outward draughts, but immediately closed by inward ones. Then the impure vapors lurking near the ceiling are continually being swept away, into the current of the chimney, through this valve.