have now to be described and illustrated. We will deal with them in chapters on "the Educational Bias," "the Bias of Patriotism," "the Class-Bias," "the Political Bias," and "the Theological Bias."
THE usual appliances for warming houses, setting aside comprehensive systems, resolve themselves into open grates, close stoves, and, under special conditions, gas apparatus, and pipes for hot air or water for warming halls and passages.
For the whole of these certain general rules may be laid down:
1. More cannot be got out of any one of them than is put into it. This is an axiom which, truism as it appears, is necessary should be impressed upon the public mind, which is apt to assume that engineering skill can multiply the heating power of fuel indefinitely. Thus, materials like fire-clay, which are absorbent of heat and useful to prevent its escape, and retain it till needed, must abstract it first from the fuel before it can dispense it.
2. There are but 100 degrees of percentage. This simple fact should be kept in mind in considering methods of saving fuel, the inventors of which would otherwise persuade one that reference to coal-merchants is a work almost of supererogation.
3. Some proportion of the heat generated must be expended in maintaining a draught in the flue, which is to carry off the products of combustion. This is by no means unprofitably lost, since it promotes ventilation as well.
4. To minimize this proportion of escaping heat to as nearly as possible what is just necessary, and to take toll from it during its passage, as by warming the air which is to replace that abstracted by the flue, are the principal directions which efforts to economize fuel should take.
5. The products of combustion, being noxious, must be wholly removed, unless they can be chemically transformed. It is as barbarous to allow the fumes from gas to invade rooms, as it is to let the door be the sole outlet for peat-smoke in an Irish cabin, or as it was to provide only louvers in the roofs of the halls of our forefathers for the smoke of their wood-fires. The evil may be disguised, but the poison is the more insidious from being comparatively unfelt. The lungs of the living animals, as the leather of dead ones on the book-shelves, become corroded alike by its pernicious influence.
6. Warming and ventilation are so intimately connected that, although the latter is not my special subject upon this occasion, it is