The following rule for proportioning the Quantity of Light for a room agrees very well with our own observations, and is very convenient for use. Divide the number of square feet contained in the room by 45, and the quotient is the least width ́ for the windows in feet; and may be divided into such a number of windows as is convenient.

But, if the windows extend down nearly to the floor, divide by 60 instead of 45.

Example. If a room be 30 feet in length, and 20 feet in width, then 30 x 20 600, which is the number of square feet in the area of the room; and, 600 divided by 45, gives 13 feet 4 inches for the sum of the widths of the windows, and may be divided into three windows of 4 feet 6 inches each. If the same room had windows extending down to the floor, 10 feet would be sufficient for the sum of the widths of the windows; and, provided less than this proportion of light be not given, the windows may be of any suitable proportions for appearance.

Parts of Windows.

88. Figure 1, plate LVII, shows the external elevation of a sash-window, where T is the top rail of the sash, M the meeting bars, B the bottom rail, and S, S the stiles.

Fig. 2 is a section of the meeting bars, with a small portion of the stiles fixed to each. Fig. 3 shows a section of an upright bar with a cross bar inserted, but not driven close; our object being to show, in a clear manner, the method of framing the bars by means of dowels; the pin, D, is called a dowel. The parts which are cut away, on the moulded sides of the upright bar, are called the franking. The object in this joint is to preserve the upright bar as strong as possible, and yet insert the cross bars, so that the moulding may not be liable to break off at the edge.

Fig. 4 shows the bars when joined.

Fig. 5 is the section of one of the bars, being called astragal and hollow.

Fig. 6 is a section of one of the stiles of the sash, with its astragal and hollow mouldings.
Fig. 7 shows a section of the top rail; and fig. 8 of the bottom rail of the sash.
Fig. 9 is a plane diminished bar, such are frequently used for shop-fronts.
Fig. 10 is a section of a bar with a Gothic point, instead of an astragal.

Construction of Circular Sashes in Circular Walls.

89. TO FORM THE COT-BAR OF THE SASH.-Figure 1, plate LVIII, is an elevation of the window. Divide the half arc of the cot-bar, PR, into any number of equal parts, as six; and, from the points of division, draw perpendiculars to the horizontal line ag; transfer the parts of the horizontal line ab, bc, cd, &c. to fig. 2, from 0 to 1; 1, 2; 2, 3; 3, 4; &c., to 6; and reverse the order from the central point 6; then draw perpendiculars upwards from these points: and make the heights of the perpendiculars, fig. 2, to correspond to the distances taken from the plan, fig. 1. Through all the points draw curves, which will give the form of the mould for the veneers for glueing up the bar in thicknesses sufficiently near for practice.

99. To form the Head of the Sash.-Divide the elevation round the outer edge into any number of equal parts, and draw lines perpendicular to the springing line from each division to the chord of the half plan. From the points where these lines intersect the chord of the half plan, draw ordinates, perpendicular to the chord of the half plan. Make the ordinates FI, GK,

• It is of some importance to attend to the circumstance, that a window is charged as two windows for the window-tax, if it be more than 4 feet 9 inches in width, unless its height be less than 3 feet 6 inches.