The great organ of the Music Hall is a choir of nearly six thousand vocal throats. Its largest windpipes are thirty-two feet in length, and a man can crawl through them. Its finest tubes are too small for a baby's whistle. Eighty-nine _stops_ produce the various changes and combinations of which its immense orchestra is capable, from the purest solo of a singing nun to the loudest chorus in which all its groups of voices have their part in the full flow of its harmonies. Like all instruments of its class, it contains several distinct systems of pipes, commonly spoken of as separate organs, and capable of being played alone or in connection with each other. Four _manuals_, or hand key-boards, and two _pedals_, or foot key-boards, command these several systems,--the _solo_ organ, the _choir_ organ, the _swell_ organ, and the _great_ organ, and the _piano_ and _forte_ pedal-organ. Twelve pairs of bellows, which it is intended to move by water-power, derived from the Cochituate reservoirs, furnish the breath which pours itself forth in music. Those beautiful effects, for which the organ is incomparable, the _crescendo_ and _diminuendo_,--the gradual rise of the sound from the lowest murmur to the loudest blast, and the dying fall by which it steals gently back into silence,--the _dissolving views_, so to speak, of harmony,--are not only provided for in the swell-organ, but may be obtained by special adjustments from the several systems of pipes and from the entire instrument. It would be anticipating the proper time for judgment, if we should speak of the excellence of the musical qualities of the great organ before having had the opportunity of hearing its full powers displayed. We have enjoyed the privilege, granted to few as yet, of listening to some portions of the partially mounted instrument, from which we can confidently infer that its effect, when all its majestic voices find utterance, must be noble and enchanting beyond all common terms of praise. But even without such imperfect trial, we have a right, merely from a knowledge of its principles of construction, of the preeminent skill of its builder, of the time spent in its construction, of the extraordinary means taken to insure its perfection, and of the liberal scale of expenditure which has rendered all the rest possible, to feel sure that we are to hear the instrument which is and will probably long remain beyond dispute the first of the New World and second to none in the Old in the sum of its excellences and capacities.