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This point being settled, we may cut out the side boards and prepare the blocks for one of our divisions, let us say the middle section, from Clef F sharp to the natural below Foot C. Blocks of this moderate size will be best made by taking a piece of wood of suitable character, long enough for six or more, and by dressing it down as each block is cut off, making careful and constant use of the gauge, the square, and the callipers. We like to form the throat with a centre-bit after the pipe is put together. The thirty-six boards will be glued to the eighteen blocks, and while the glue is drying we can prepare the backs and fronts. The bevelled lip of the latter will be left uncut until all the pipes have been glued up and dressed over, and the top edges nicely cleaned off and made true. But as there will be, doubtless, a most pardonable anxiety to hear the sound of one pipe, we will here explain that the height of the mouth of each pipe must be equal to one-third of its width; thus the mouth of the pipe measuring one inch and a half across the block (A in our scale) will be ½ inch in height. In measuring the height of the mouths, a pair of proportional compasses with sliding centre, or common dividers set to thirds, fourths, and fifths, will be useful if not necessary. The slope of the bevel is not of great importance. Cut it with a sharp chisel, taking care not to injure the block, and leave the lower edge or lip rather blunt. A sharp and pointed knife may be employed in cutting the lip truly, guided by the square. The use of fine glass-paper is permissible here to smooth all these parts nicely.