1. The sound-board is a shallow box, divided internally into as many transverse grooves or channels as there are notes on the key-board. The pipes stand upon holes bored through the top of the box into these channels; and it is plain that if air is made to fill these channels, and to issue from these holes in a constant stream when we please, all the pipes which stand upon the holes will give their sounds according to their pitch and character.
_Remark._--Thus if one channel, say the channel corresponding to Tenor C, have five holes bored into it through the top of the box, then five pipes standing upon those holes may be made to speak at once, or in chorus, by pressing down the one key on the manual.
2. It is plain that we must possess the power of opening and closing these holes in sets or classes at our pleasure, so that the air may be directed into those pipes which we desire to hear, while others are silent. The top of the box is therefore made double, or of two layers of wood; and between the two layers long strips of thin wood are introduced, lying lengthwise, that is to say, at right angles to the channels beneath or within. The holes are bored down through all these three layers of wood forming the top of the box; and we see that by sliding the thin slip an inch or so to the right or left, we can cut off at once the current of air from the pipes standing on those holes, since the apertures in the three layers will then no longer coincide.
_Remark._--All this is quite independent of, and preliminary to, the arrangements for admitting the supply of air to the channels themselves.
3. Having already made our Stopped Diapason pipes, let us range them on a table or floor, and consider well how they must be planted on a sound-board such as we are about to make for our organ, be it broad and shallow, or narrow and deep, be it low or lofty.
_Remark._--No other stop will practically take up so much room on the sound-board as the Stopped Diapason; hence, if we plot the board with reference to it, all the other pipes will be easily worked in.
4. On the opposite page several different plantations of the Stopped Diapason are shown both in elevation and in plan. In Fig. 5 the pipes, planted in a double row throughout, are placed alternately to the right and to the left, meeting in the middle at the smallest pipe. The exact reverse of this plantation, namely, placing the largest pipes in the middle, and sloping down to the smallest pipes at each end, can be easily imagined, and it is unnecessary to figure it. It is clear that in both these plantations the large pipes occupy a space, as regards depth, out of proportion to the space occupied by the upper part of the stop. Fig. 6 shows a very common plantation of pipes, which, as we shall see hereafter, allows us to simplify the internal mechanism or action. Fig. 7, in plan only, shows a mode of economising space as regards depth by planting the pipes of the lower octave in a single row, resuming the double row at Tenor C. This plantation would suit a wide and shallow organ. Figs. 8 and 9 show different methods of planting the large pipes in order to avoid a disproportionate sacrifice of space on the board. It will be seen at a glance that they can be ranged behind the pipes of the tenor and treble octaves, or carried off to the right and left in rows standing at right angles to them. Fig. 10, in elevation only, shows how we may build an organ under the ceiling of a very low room, by planting the eight feet octave on a board of its own at a lower level than that of the sound-board proper. And it is easy to conceive, without a figure, that this accessory board may be replaced by two boards, to right and left, resulting in a plan resembling that in Fig. 9, but giving a lower level to the tall pipes.