Different professors of ventriloquism have given different accounts of the manner in which they succeeded in producing their illusions. Baron Mengen, one of the household of Prince Lichtenstein, at Vienna, said that it consisted in a passion for counterfeiting the cries of animals and the voices of different persons. M. St. Gille referred his art to mimicry; and the French Academy, combining these views, defines the art as consisting in an accurate imitation of any given sound as it reaches the ear. Scientific solutions are various. Mr. Nicholson thought that artists in this line, by continual practice from childhood, acquire the power of speaking during inspiration with the same articulation as the ordinary voice, which is formed by expiration. M. Richerand declares that every time a professor exhibits his vocal peculiarities, he suffers distension in the epigastric region; and supposes that the mechanism of the art consists in a slow, gradual expiration, drawn in such a way, that the artist either makes use of the influence exerted by volition over the parietes of the thorax, or that he keeps the epiglottis down by the base of the tongue, the apex of which is not carried beyond the dental arches. He observes, that ventriloquists possess the power of making an exceedingly strong inspiration just before the long expiration, and thus convey into the lungs an immense quantity of air, by the artistical management of the egress of which they produce such astonishing effects upon the hearing and imagination of their auditors. The theory propounded by Mr. Gough in the "Manchester Memoir," on the principle of reverberated sound, is untenable, because ventriloquism on that theory would be impossible in a crowded theatre, which admits not of the predicated echoes. Mr. Love, in his account of himself, asserts a natural aptitude, a physical predisposition of the vocal organs; which, in his case, discovered itself as early as the age of ten, and gradually improved with practice, without any artistic study whatever. He states that not only his pure ventriloquisms, but nearly all his lighter vocal imitations of miscellaneous sounds, were executed in the first instance on the spur of the moment, and without any pre-meditation. The artist must evidently possess great flexibility of larynx and tongue. Polyphony, according to our modern professor, is produced by compression of the muscles of the chest, and is an act entirely different from any species of vocal deception or modulation. There is no method, he tells us, of manufacturing true ventriloquists. Nature must have commenced the operation, by placing at the artist's disposal a certain quality of voice adapted for the purpose, as the raw material to work upon. It is like a fine ear or voice for singing--the gift of Nature. It follows, therefore, that an expert polyphonist must be as rare a personage as any other man of genius in any particular art. THE INCENDIARY.