should be removed by cutting steps so that the foundation stones shall lie upon horizontal beds.

Foundations are frequently impaired by the slow, insidious action of springs or of water percolating from the canal which supplies the water power for the mill; and the proper diversion of such streams should be carefully provided for.

In the question of foundations, there is much of a general nature which is applicable to all structures; but, at the same time, each case requires independent consideration of the circumstances involved.

WALLS.

In addition to what has been said, there is but little for me to offer on the subject of walls beyond the general question of stability. In mill construction, walls of uniform thickness have been displaced by pilastered walls, about sixteen inches thick at the upper story, and increasing four inches in thickness with each story below.

The remainder of the walls is from four to six inches less in thickness than at the pilasters. Frequently the outside dimensions of these pilasters are somewhat increased, giving greater stability and artistic effect. By leaving hollow flues within them, and using these flues as conductors for heated air which may be forced in by a blower, such pilasters afford a means for the most efficient method of warming the building.

Consideration must be given to the contraction of brick masonry, especially when an extension or addition is to be made to an older building. This shrinkage amounts to about three-sixteenths of an inch to the rod, an item which is of considerable importance in the floors of high buildings, where the aggregate difference is very appreciable. Some degree of annoyance is caused by neglect to consider this element of shrinkage in reference to the window and door frames, which should have a slight space above them allowing for such contraction. This contraction is often the source of serious trouble in brick buildings with stone faces, the shrinkage of the brick imposing excessive stress on the stone. Instances of this are quite frequent, especially in large public buildings, notably the capitol at Hartford and the public building at Philadelphia, where the shivering of the joints of the stone work gave undue alarm, on the general assumption that it indicated a dangerous structural weakness. The difficulty has, I believe, been entirely remedied in both cases.

The limit of good practice on loads upon brickwork is eight to ten tons per square foot, although it is true that these loads are largely exceeded at times. It is not to be shown, however, that the limits of safety in regard to desirable construction should be confined to the use of masonry for any low buildings. Structures which may be said to be equal to those of brickwork, as far as commercial risk is concerned, can be built wholly or in part of wood so as to conform to all practical conditions of safety. This statement does not apply except to low buildings of one or possibly two stories in height, where the timber cannot be subjected to the intense blast of flame occurring when a high building is on fire.

Mr. George H. Corliss, the eminent engine builder, of Providence, first built a one-story machine shop, with brick walls extending only to the base of the windows, above this the windows being very close together, with solid timber construction between them.

Another method is to place upright posts reaching from the sill to the roof timbers, and to lay three-inch plank on the outside of such posts up to the line of the windows. A sheathing on the outside plank between the timbers is laid vertically and fastened to horizontal furring strips. In some instances a small amount of mortar is placed over each of the furring strips. The reason for this arrangement is to prevent the formation of vertical flues, which are such a potent factor in the extension of fires.

WINDOWS.

Light is often limited or misapplied on account of faulty position or size of windows. The use of pilastered walls permits the introduction of larger windows, which are in most instances virtually double windows, the two pairs of sashes being set in one frame separated by a mullion. A more recent arrangement, widely adopted in English practice, is to place a swinging sash at the top of the window, which can be opened, when necessary, to assist in the ventilation, while the main sashes of the window are permanently fixed.

Rough plate glass is used in such windows, because it gives a softer and more diffused light, which is preferred to that from ordinary clear glass. White glass may be rendered translucent by a coat of white zinc and turpentine.

The top of a window should be as near the ceiling as practicable, because light entering the upper portion of a room illuminates it more evenly, and with less sharply marked shadows, than where the windows are lower down.

The walls below the windows should be sloped, in order that there may be no opportunity to use them as a resting place for material which should be placed elsewhere.

FIRE WALLS.

Brick division walls should be built so as to constitute a fire wall wherever it is practicable to do so. Such walls should project at least three feet above the roof, and should be capped by stone, terra cotta, or sheet metal. They must form a complete cut-off of all combustible material, especially at the cornices.

FIRE DOORS.

All openings in such walls must be provided with such fireproof doors as will prove reliable in time of need. Experience with iron doors of various forms of construction show that they have been utterly unreliable in resisting the heat of even a small fire. They will warp and buckle so as to open the passageway and allow the fire to pass through the doorway into the next room.

A door made of wood, completely enveloped by sheets of tinned iron, and strongly fastened to the wall, has proved to resist fire better than any door which can be applied to general use. I have seen such doors in division walls where they had successfully resisted the flame which destroyed four stories of a building filled with combustible material, without imposing any injury upon the door except the removal of the tin on the sheet iron; and the doors were kept in further service without any repairs other than a coat of paint.

The reason for this resistance to fire is that the wood, being a poor conductor of heat, will not warp and buckle under heat, and cannot burn for lack of air to support combustion. A removal of the sheet metal on such a door after a fire in a mill shows that the surface of the wood is carbonized, not burned, reduced to charcoal, but not to ashes.

Many fire doors are constructed and hung in such a manner that it is doubtful whether they could withstand a fire serious enough to require their services.

The door should be made of two thicknesses of matched pine boards of well dried stock, and thoroughly fastened with clinched nails. It should be covered with heavy tin, secured by hanging strips, and the sheets lock-jointed to each other, with the edge sheets wrapping around, so that no seam will be left on the edge.

Sliding doors are preferable to swinging doors for many reasons, especially because they cannot be interfered with by objects on the floor. But, if swinging doors are used, care should be taken that the hinges and latches are very strong, and securely fastened directly to the walls, and not to furring or anything in turn attached to the walls. The portion of the fixtures attached to the doors must be fastened by carriage bolts, and not by wood screws.

Sliding on trucks is the preferable method of hanging sliding doors, inclined two and one half inches to the foot, and bolted to the wall. The trucks should be heavy "barn door hangers," bolted to the door; and a grooved door jamb, of wood, covered with tin similar to the door, should receive it when shut. A step of wood will hold the door against the wall when closed. A