Act
2 of the 7 encyclopedias on this shelf carry an entry for Act. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
in the presentation of drama, one of the main divisions of a play, in which a definite portion of the action is completed. The divisions of drama into act and scene may mark a change of time or place. They give relief to both actors and audience from the strain of a long play, and also afford opportunity for change of costume and scenery. The unities of the Greek drama made separation into acts unnecessary. The Roman theater first adopted the division of a play into acts, and made five the regular number. Horace mentions this as a fixed rule, and it was obeyed by all dramatists of the Renaissance. Shakespeare, who paid little attention to any of the accepted rules of dramatic art, invariably divides his dramas into five acts. In light comedy, the rule is no longer regarded as essential; but in tragedy, where the action is weighty, there seems to be a real reason for the five acts. In every great action, there are naturally three parts, the introduction, the climax, and the conclusion. By presenting the introduction, or causes leading to the climax, in two acts instead of one, the characters are better developed, the interest is deepened, and the climax, being in a measure anticipated, is more impressive. So two acts leading from the climax to the final catastrophe allow the mind of the spectator to grasp more fully the sadness and horror of the situation, and thus those emotions which real tragedy should arouse are more deeply stirred. See Drama ; Tragedy ; Comedy ; Scene ; Stage
Collier's New Encyclopedia (1921)
in dramatic language, a portion of a play performed continuously, after which the representation is suspended for a little. As early as the time of Horace there were five acts in a drama, but this number is frequently modified on the modern stage. In parliamentary language, an act of congress, legislature, etc. In law: (1) Anything officially done by the court, as the phrases "Acts of Court," "Acts of Sederunt," etc. (2) An instrument in writing for declaring or proving the truth of anything.