As we return to the impression produced by the grand _facade_, we are more and more struck with the subtile art displayed in its adaptations and symbolisms. Never did any structure we have looked upon so fully justify Madame de Stael's definition of architecture, as "frozen music." The outermost towers, their pillars and domes, are all _square_, their outlines thus passing without too sudden transitions from the sharp square angles of the vaulted ceiling and the rectangular lines of the walls of the hall itself into the more central parts of the instrument, where a smoother harmony of outline is predominant. For in the great towers, which step forward, as it were, to represent the meaning of the entire structure, the lines are all curved, as if the slight discords which gave sharpness and variety to its less vital portions were all resolved as we approached its throbbing heart. And again, the half fantastic repetitions of musical forms in the principal outlines--the lyre-like shape of the bases of the great towers, the harp-like figure of the connecting wings, the clustering reeds of the columns--fill the mind with musical suggestions, and dispose the wondering spectator to become the entranced listener. The great organ would be but half known, if it were not played in a place fitted for it in dimensions. In the open air the sound would be diluted and lost; in an ordinary hall the atmosphere would be churned into a mere tumult by the vibrations. The Boston Music Hall is of ample size to give play to the waves of sound, yet not so large that its space will not be filled and saturated with the overflowing resonance. It is one hundred and thirty feet in length by seventy-eight in breadth and sixty-five in height, being thus of somewhat greater dimensions than the celebrated Town Hall of Birmingham. At the time of building it, (1852,) its great height was ordered partly with reference to the future possibility of its being furnished with a large organ. It will be observed that the three dimensions above given are all multiples of the same number, thirteen, the length being ten times, the breadth six times and the height five times this number. This is in accordance with Mr. Scott Russell's recommendation, and has been explained by the fact that vibrating solids divide into _harmonic lengths_, separated by _nodal points_ of rest, and that these last are equally distributed at aliquot parts of its whole length. If the whole extent of the walls be in vibration, its angles should come in at the nodal points in order to avoid the confusion arising from different vibrating lengths; and for this reason they are placed at aliquot parts of its entire length. Thus the hall is itself a kind of passive musical instrument, or at least a sounding-board, constructed on theoretical principles. Whatever is thought of the theory, it proves in practice to possess the excellence which is liable to be lost in the construction of the best-designed edifice.