In theory, the ecstatic trance is involuntary, although certain conditions are recognised as being specially favourable to its occurrence. “It comes to a man through vision of the majesty of God and through revelation of the divine omnipotence to his heart.” Such, for instance, was the case of Abū Hamza, who, while walking in the streets of Baghdād and meditating on the nearness of God, suddenly fell into an ecstasy and went on his way, neither seeing nor hearing, until he recovered his senses and found himself in the desert. Trances of this kind sometimes lasted many weeks. It is recorded of Sahl ibn ʿAbdallah that he used to remain in ecstasy twenty-five days at a time, eating no food; yet he would answer questions put to him by the doctors of theology, and even in winter his shirt would be damp with sweat. But the Sūfīs soon discovered that ecstasy might be induced artificially, not only by concentration of thought, recollection (_dhikr_), and other innocent methods of autohypnosis, but also by music, singing, and dancing. These are included in the term _samāʿ_, which properly means nothing more than audition. That Moslems are extraordinarily susceptible to the sweet influences of sound will not be doubted by any one who remembers how, in the _Arabian Nights_, heroes and heroines alike swoon upon the slightest provocation afforded by a singing-girl touching her lute and trilling a few lines of passionate verse. The fiction is true to life. When Sūfī writers discuss the analogous phenomena of ecstasy, they commonly do so in a chapter entitled ‘Concerning the _Samāʿ_.’ Under this heading Hujwīrī, in the final chapter of his _Kashf al-Mahjūb_, gives us an excellent summary of his own and other Mohammedan theories, together with numerous anecdotes of persons who were thrown into ecstasy on hearing a verse of the Koran or a heavenly voice (_hātif_) or poetry or music. Many are said to have died from the emotion thus aroused. I may add by way of explanation that, according to a well-known mystical belief, God has inspired every created thing to praise Him in its own language, so that all the sounds in the universe form, as it were, one vast choral hymn by which He glorifies Himself. Consequently those whose hearts He has opened and endowed with spiritual perception hear His voice everywhere, and ecstasy overcomes them as they listen to the rhythmic chant of the muezzin, or the street cry of the saqqā shouldering his water-skin, or, perchance, to the noise of wind or the bleating of a sheep or the piping of a bird. Pythagoras and Plato are responsible for another theory, to which the Sūfī poets frequently allude, that music awakens in the soul a memory of celestial harmonies heard in a state of pre-existence, before the soul was separated from God. Thus Jalāluddīn Rūmī: