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Wooden pipes are also made with inverted mouths, that is to say, the bevelled lip is formed on the inside instead of on the outside of the front board. In this case the bevel is cut and the mouth measured and formed before the pipe is put together, and the front board will be of the same length as the others, and will be glued like them to the block. The throat is cut through the board into the block, and the cap will project beyond the level of the board. All this is shown in Fig. 4.

Fig. 4.

We have a very charming Stopped Diapason made in this way, and with perforated stoppers, in one of our organs. It is of red cedar from Middle C to top; the lower part is of pine and of the ordinary construction. The mouths are in the proportion of two-sevenths of the width of each pipe. Inverted mouths are well suited, also, to the Clarabella and Hohl Flöte, two kindred stops which sometimes take the place of the Stopped Diapason in its upper octaves. The pipes are open, and have a hollow penetrating tone; Middle C is 2 feet long, and its block may be of the same size as that of the same note in our scale, namely, about 1⅜ by 1¾. The mouth about 2⁄7 of the width. These open pipes are tuned by means of shades, which are pieces of pipe metal let into a saw-cut made in the top edge of the back board. The shade must be as wide as the pipe, and ½ inch longer than its depth. The pipe is flattened by bending the shade over the open top, sharpened by raising it.