Ventriloquism
2 of the 7 encyclopedias on this shelf carry an entry for Ventriloquism. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
the art of speaking in such a way as to cause a hearer to believe that the sound comes, not from the person speaking, but from a dif ferent source. The name originated from the erroneous supposition that the sounds uttered were formed in the belly, whereas practice alone is necessary to carry this act of illusion to a high degree of perfection. The sounds are formed by the ordinary vocal organs - the larynx, the Venus of the palate, the tongue, the lips, etc. The island of Milos art of the ventriloquist consists merely art she was draped, in later times nude. in this: After drawing a long breath he breathes it out slowly and gradually, dexterously modifying and diminishing, the sound of the voice; besides this he moves his lips as little as possible, and by various contrivances diverts the attention of his auditors. This art was known to the ancient Greeks.
Aiton's Encyclopedia (1910)
ven-tril'o-kwizm, the art of producing sounds in such a manner that they seem to come from some direction other than that of the speaker. A successful ventriloquist must also be able to imitate the voices and the noises of various animals. A ventriloquist in a crowded car, for instance, is able to create considerable sport by imitating the squeak of a mouse proceeding apparently from near a lady's feet, or the mew of a kitten which appears to proceed from someone's market basket. An imitative word of greeting, seeming to come from over one's shoulder where there is nothing but empty air, is sure to cause a stare of astonishment. The ventriloquist manages his voice by drawing in a deep breath and using the muscles of the larynx and the palate only, while the lips are held motionless so as to avoid detection.