of concrete, a very ancient plan, and not modern, as is commonly supposed. The Romans frequently used concrete walls in their aqueduct bridges and other constructions. The cement used was of extraordinary hardness, and has, I believe, never been surpassed, even if equaled, in later times. It might be called the "cement of the Romans," as the term "Roman cement" is now commonly applied to a very inferior article. In making concrete columns, the Romans adopted the practice of inserting layers of their flat bricks, which we should perhaps call tiles, at intervals, and they faced the surface with stones, generally disposed after the fashion known as opus reticulatum. This consisted in placing small cubical blocks of stone against the surface of the concrete, so that the sides of the exposed faces were not vertical and horizontal, but the diagonals were, thus giving the appearance of network, or of a chess-board set up on one corner. These devices assisted greatly in protecting the structure

from the weather, and from rough usage. Such walls may also be very well faced with tiles of various kinds.

The chimney flues should be as straight as possible. They should be separate from one another a matter very often not attended to-and they are better lined with pipes, as these are much more easily cleaned; an updraught is more readily established in them, and they completely disconnect the flue from the structure of the house, and so help to prevent destruction by fire.

It is important that the chimneys should be higher than the surrounding buildings, so that the wind may pass freely over them, and that they may not be sheltered from its action in any direction whatever. If this is not the case, there will be a down draught in the chimneys when the wind is in a certain direction, and the more the chimneys are sheltered by high buildings the more chances there are of down-draughts in them. If necessary, an iron or zinc pipe

called a "tall-boy," may be placed on the top of the brickwork, to increase the length of the flue. This is sometimes even carried up adjoining buildings, and is, as a general rule, better without a cowl of any kind on the top of it, as will be further explained in the next lecture.

Flooring.-Fire-proof floors are most desirable. They may be made of concrete or brick arches between iron girders, in which case there is no space between the flooring of one room and the ceiling of the room below. When timber is used, it should be dry and well-seasoned, with sound boarding, to ensure a separation between the rooms, and to prevent either water leaking from the floor to the ceiling below, or air passing from the room below to that above. Good flooring evidently serves to protect the ceilings of rooms below. Where there is space between the flooring and the ceiling, and still more especially where a wooden flooring is placed over a concrete or other foundation laid on the ground, it is necessary

to provide for ventilation of the space below the flooring. This is usually done by placing a perforated iron grating, instead of a brick, here and there, in the outer walls, so that air can pass freely in or out below the floors. For this pur

pose bricks, such as those exhibited, with conical holes through them, would no doubt be found very useful.

The Roof. This may be constructed either of fire-proof materials, or of

timber, and in either case may be

covered with slates or tiles, or may be thatched; copper or corrugated iron are also used. Sometimes zinc is used on account of its cheapness. It is not a good material, as it does not last long. Lead is largely used, especially upon flat roofs, and is valuable an account of its lasting properties. Where there are eaves, it is important that they should not drip on to the walls, but project, so as to throw the water off. Cornices and all projections should be constructed so as to throw off the rain, or it will run down the walls. If this is not done, the

walls will be continually damp and dirty. Rain-water gutters may be made of lead or iron. They must have a sufficient fall, and shoot directly into the heads of the rain-water pipes. They should be wide enough inside to stand in, so that the snow may be cleared out. If this is not done, it will accumulate, blocking up the channel, and when the thaw comes the melted snow will work its way through the tiles or slates of the roof, and injure the ceilings below.* Rain-water gutters should not be carried through the house from one side to the other, and especially not through bedrooms. Nor should they be carried, as is sometimes done, round the house inside the walls, and through the rooms. A more or less disagreeable smell is frequently noticed in rooms through which rain-water gutters pass. The rain-water pipes should also be outside the house. They should be of iron, well jointed. Galvanized iron ones are preferable; they are only a

* The remark as to the width of gutters does not apply to eaves-gutters.