this again is covered by another box large enough to leave an air space of about three inches between the two, on all sides.

For the office rooms the pipes may be of rectangular form, concealed by suitable architectural finish of the ceiling, in which lateral openings for registers may be made. Or, proper air ducts may be formed in the side walls and the registers placed at suitable intervals. Or, again, the pipes may be carried around inside the walls, close to the ceilings, and registers located in the same manner.

There may be for this system the double-duct arrangement. That is,

two sets of pipes or ducts, one carrying cold and one warm air, the registers being so arranged that they will furnish one or the other, or a mixture of both, by means of what is technically known as a "mixing damper."

In offices and rooms of moderate size which are heated by warm air being forced into them near the ceiling, it is usual to provide means of escape for the air as it cools and descends to the floor, through grated openings placed two or three feet from the floor, and connected with flues or ducts leading to the roof. But in offices where doors are frequently opened this does not seem to be necessary, the matter of ventilation being of small consequence compared to that of heating.

The forge shop and various other buildings require no special arrangements for heating. The water-closet rooms may be warmed sufficiently by providing grated openings in the wall dividing them from the boiler room. They should be near the ceiling, on each floor.

The question of proper temperature of shops where men are at active work should be considered as quite different from providing for heating a factory where the work is usually much lighter, the number of employees per hundred feet of floor space much greater, and frequently a large proportion

of them females.

In a machine shop devoted to a medium class of work, a temperature of about 60 degrees will be found generally comfortable to the majority of the men. We have known of shops where the temperature seldom went above 50 degrees in cold weather, and there was no complaint. The former figure will, however, be more satisfactory.

The temperature in the storeroom, tool room, and pattern shop will need to be about 65 degrees, and in the drawing room and offices, between this and 70 degrees. Unless the ventilation is very carefully attended to, there is more danger in having these latter rooms too warm than not warm enough, and any system of heating which does not recognize the importance of good and thorough ventilation is radically wrong in both theory and practice.

CHAPTER XIII

THE SYSTEM OF LIGHTING

Natural and artificial lighting. Forms and proportions of windows. Different kinds of glass. Position of windows. Diagrams illustrating various forms of lighting. The width of windows. Benedict's system of window construction, with illustrations. The good features of the plan. Skylights. Translucent substitute for glass. Shades and curtains. Artificial light. The hours of lighting by artificial light. Systems of artificial light. Electricity the most useful. Some of the old-time methods of lighting. To have light we must submit to heat. Arc lights versus incandescent lights. Advantages and disadvantages. Portable electric lights. Both arc and incandescent lights. should be used. The dynamos. Distribution of lights. In the machine shop. The traveling crane space must be left unobstructed. In the galleries. In the foundry. Arc In the forge shop. In the storehouse and carpenter shop. In the engine room. lights in the yard. In the office building. Number of lights for the entire plant. Power necessary to supply the current. General arrangement shown in the plans.

THE heating and ventilation of our manufacturing buildings having been duly provided for in the last chapter, the next question of importance to be considered is that of lighting, which forms the subject of the present chapter.

In considering the matter of lighting manufacturing buildings we may properly divide the subject into two parts. The first of these relates to the utilization and management of the sunlight for our use during the daytime; and the second, to the artificial light which we must provide in the absence of sunlight and in the dark and obscure corners, of which there should be as few as possible in the modern shop.

For properly lighting a shop during the daytime, many forms and proportions of windows have been devised, from those of small area and diminutive lights of glass, to those very high and narrow; those broad and low; those of large area placed far apart; those of much less area placed near together; those covering almost the entire wall with glass area; those placed vertical and those in an inclined position; those placed as skylights in the roof; and those placed in the ventilating space at the top or ridge of the roof.

Again, as to the kind and quality of glass used. Some prefer the ordinary plain glass, admitting a flood of light, regulating it by means of shades or curtains. Others use the same glass, "stippling" the surface with white zinc thinned with spirits of turpentine to relieve the eyes of the glaring light. Again,

ground glass is used. Still others prefer the rough cast or "cathedral" glass, as it is sometimes called.

What is called "ribbed glass," with the ribs or ridges running in a horizontal direction, is probably better than either. One inventor proposes to construct windows composed of a series of round rods of glass placed closely together, and states that one of its advantages is that if broken by a flying chip, or in any similar manner, only one or at most a few of the rods will be injured, and these may be easily and cheaply replaced.

In reviewing these various methods of construction it may be said that broad and low windows in the side walls will light the bench at the wall and perhaps one or two rows of machines, while the center of the room receives little or no illumination. This condition is sometimes sought to be remedied by the use of skylights in the roof.

Windows placed too high in the side walls will light the center of the room but leave the benches around the walls in the shadows of the high window sills. Therefore it is proper to so locate the window sill as to afford proper light at the bench vises; then to continue the window well up to the ceiling in order that the whole room may receive, as nearly as may be, an equal quantity of light.

In order that one may get a clear idea of the difference in the capacity of the various heights, positions, and angles of windows, several diagrams are presented to illustrate the matter.

Fig. 66 shows a cross-section of wall with the work bench in proper position, and the room lighted with one of the older styles of windows, which were

-21 ft:

FIG. 66. Lighting Diagram. Low Windows.

25 ft.

FIG. 67. Lighting Diagram. High Windows.

placed considerably lower than is now the practice. It will be noticed that the rays of light entering at an angle of 30 degrees, the highest beam of light will touch the floor at a distance of 21 feet.

Fig. 67 shows a similar cross-section with the window placed high up, and it will be seen that the distance reached by the light is 25 feet, or about 20 per cent farther. At the same time the work which the machinist is doing at the bench is properly illuminated.

Fig. 68 shows a cross-section through the machine shop, and gives the

floor surfaces illuminated by parallel beams of light at various angles. It should be understood, of course, that in all these cases light is not confined to these surfaces, since it is always more or less strongly diffused over a much larger space. These diagrams are only intended to show the relative amount of illumination.

FIG. 68. Lighting Diagram. Section through the Machine Shop.

Fig. 69 is a cross-section of the newer form of saw-tooth roof construction, and illustrates the largely increased amount of surface lighted up by this method, which is now generally regarded as the best method of lighting up large areas in one-story shops. In this system of lighting the windows should face towards the north.

The width of the windows and their distance apart is a matter of great difference of opinion. Where the construction is of steel or wood they may be placed less than two feet apart, if it seems necessary to do this. Where brick walls are used the distance should generally be more, depending, of course, on the entire height of the wall.

FIG. 69.-Lighting Diagram. The Saw-tooth Construction of Roof.

In our arrangement of the windows in the machine shop (as given in Chapter II) the size is 4 feet wide and 10 feet high. These figures are the dimensions of the inside of the sashes, therefore providing 40 square feet of glass. This will make the opening in the wall nearly 5 feet wide, which, with bays of 18 feet 3 inches centers, two windows to each bay, will give about 4 feet 2 inches of brickwork between the windows. This will give sufficient