In our arrangement of the windows in the machine shop (as given in Chapter II (General Plans)) 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 strength to the side walls, and will also provide quite enough light for all ordinary classes of machine shop work to be done in such a building.

Lighting Diagram. The Saw tooth Construction of Roof.

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

In reference to the details of construction of the windows of machine shops and factory buildings, Mr. Edwy E. Benedict, of Waterbury, Conn., a successful designer of factory buildings, has adopted the plan of having in each window three sashes, each containing two lights of glass. In the case illustrated they are of 24 x 24 glass, making a window of 4 x 6 feet, as shown in front elevation in Fig. 70. An outside elevation of the upper portion is shown in Fig. 71; a horizontal section of one jamb, with sash, glass, weather strips, etc., in Fig. 72; an inside elevation, showing the inside finish at the top and bottom, in Fig. 73; and a vertical cross-section in Fig. 74.

Outside Elevation of Benedict's Shop Window.

Fig. 70. Outside Elevation of Benedict's Shop Window.

Outside Elevation of upper portion.

Fig. 71. Outside Elevation of upper portion.

Some of the good features of this plan will, no doubt, be heartily commended by practical men. For instance, in Fig. 71 it will be noticed that the flat arch on the outside face of the wall reaches down below the segment, or supporting arch, which is shown in dotted lines in this figure, and drawn in full lines in Fig. 73. The vertical section in Fig. 78 shows its office, of making the top of the window weather-tight. It will also be noticed, by reference to Fig. 72, that the side face casings are built into the brick wall for the same purpose. These points, with the use of the Tabor weather strips, make a perfectly weather-tight arrangement that will be greatly appreciated by the workmen in the shop, as well as the man who pays the coal bills. The working details are quite clearly shown in the several views.

Windows may be made of any desired height by increasing the length of the lights of glass. Thus, 24 x 36 glass would make a window 4 by 9 feet.

The bottom sash is glazed with clear glass, and the two above it with ribbed glass, the ribs running horizontal in all cases.

Skylights should not be used where they can be avoided, as they are a prolific source of leaky roofs, damage by accidental breakage, as well as numerous other difficulties, and even a light fall of snow quite destroys their lighting properties.

A translucent material formed on a fine wire netting is an excellent substitute for glass where skylights must be used. It gives a soft, diffused light and there is no danger of breakage as with glass. Windows in the ventilating portion of the roof are not only useful for lighting the central portion of the shop, but they conveniently act as ventilators when the sashes are hung on pivots and handled by cords. They may easily be so constructed as to avoid any trouble from leaking.

As to the kind of glass to be used, the plain glass is, of course, the cheapest. It must, however, be shaded by curtains, which can be readily run up and down; and these are liable to get out of orderand to require a continual expense to keep them in presentable and useful condition. The amount thus spent added to the cost of plain glass will soon pay for good ground glass which will need no curtains, and which, while rendering the light soft and agreeable to the eyes of the workmen, will also diffuse it over the area of the shop much better and more equally than the plain glass. At the same time none of the light is lost by interposed shades or curtains. As to "stippled" glass, the stipple is apt to crack and peal off, and will also absorb considerable dirt and grease, making it much more difficult to keep clean than clear or ground glass; and the repeated washings are apt to remove portions of the "stippling," leaving a patched and unsightly effect. The rough or "cathedral" glass is more expensive, not as agreeable to the eyes, and considerably lessens the volume of light. Windows of glass rods do not seem to have been sufficiently employed to demonstrate their usefulness. Ribbed glass is now quite popular for shop windows and diffuses a soft and agreeable light, and seems best adapted for the purpose.

Fig. 72. Horizontal Section of Window jamb, sash, glass, etc.

Inside Elevation, showing inside finish.

Fig. 73. Inside Elevation, showing inside finish.

We have seen shops in which practically the whole side wall was a mass of glass, only the space for the posts supporting the roof and the frames containing the sashes being opaque. Such a prodigality of light does not seem necessary in practice, and in fact it may be hurtful to the eyesight of the workmen, while the cost of construction and the continual cost of renewals and repairs of such a great quantity of glass will be a large initial expense as well as an important annual outlay. The expense of heating will also be largely increased.

Let us now consider the question of artificial light. First, the usual time during which we must provide for artificially lighting up the buildings. Omitting the six usual holidays of the year and calculating on the basis of a ten-hour day, we have 3,060 working hours in a year's work. If the working day begins at 7 A. M. and ends at 6 p. M., with one hour for dinner, we shall need artificial light, for the ordinarily well-lighted shops, for about 460 hours out of the entire 3,060 working hours of the year.