Let me digress here to answer another question.  No, don’t put your ventilating flues in the outer walls if you expect the air to rise through them in cold weather; for it will not, if they reach the moon, unless it is warmer than that lying at their base.  You may as well expect water to rise from the cistern to the tank in the attic because the pipe runs there, as that air will rise simply because there is a passage for it.  Sometimes holes are made into the chimney-flues, but this is robbing the stoves or the fireplaces.  It is better to build an independent flue so close that it shall always feel the heat from the black warm heart of the chimney, for warmed by some means it must be.  Yet warm air does not choose to rise.  It falls like lead unless lifted by something heavier than itself.

To return to the former point.  When you can warm within a ventilating flue all the air passing through it more economically than you can warm the same quantity in the room from which it is taken, then you may admit the air to feed this same flue near the bottom and perhaps save fuel; but I doubt whether the remaining air will be any purer than if an equal amount had been allowed to escape near the ceiling.  The answers to your square questions necessarily dovetail.  The hot-air registers should always be in the partitions if possible.  It saves sweeping dust into the pipes; it saves cutting the carpets; it lessens the risk of a debilitating warm bath to people addicted to standing over them; it diffuses the heat more evenly through the room; and, owing to this better diffusion, there is less waste through the ventilating outlet at the top of the room, if it should be there.

The foregoing refers to rooms heated on the furnace principle, where all that seems needful for complete ventilation is a sufficient outgoing of the air to cause a constant change.  In theory, too, the warm air must cross the room to make its exit.  Indeed, the plan of admitting it at the top and drawing the cold air from the base has been strongly urged by one of the most earnest and thoughtful advocates of thorough ventilation.  In practice, this fresh air is apt to come from the region of the coal-bin and potato-barrels, especially in very cold weather, and I doubt whether it will find the door of escape sooner at one side than another, unless immediately over the entrance.  As to your next inquiry, I do not think our winter quarters can be warmed so safely and healthfully in any other way as by steam or hot-water radiators; but the first cost of the modes now in use puts them beyond the reach of common people, the very ones who need them most.  Whether it’s the tariff on pig-iron, the patent royalties, the skilled labor, the artistic designs, the steam joints and high pressure, or all combined, that make the cost, I cannot say, but I have faith that some one of the noble army of inventors will, erelong, give us a system more economical in manufacture and simple in use than any at present known.  It will hardly bring him a fortune, however.  The real benefit to humanity will be too great for a temporal reward.  Not only will this coming system be available for cheap and isolated houses, but when they stand compactly, one boiler will send its portable caloric to the dwellers on one entire square, as gas and water are now distributed.