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 courts of law, or of the senate, meaning (1) what was done before the magistrates, the people or the senate; (2) the records of such public proceedings.

In connexion with other words “act” is employed in many phrases, e.g. act of God, any event, such as the sudden, violent or overwhelming occurrence of natural forces, which cannot be foreseen or provided against. This is a good defence to a suit for non-performance of a contract. Act of honour denotes the acceptance by a third party of a protested bill of exchange for the honour of any party thereto. Act of grace denotes the granting of some special privilege.

In universities, the presenting and publicly maintaining a thesis by a candidate for a degree, to show his proficiency, is an act. “The Act” at Oxford, up to 1856 when it was abolished, was the ceremony held early in July for this purpose, and the expressions “Act Sunday,” “Act Term” still survive.

In dramatic literature, act signifies one of those parts into which a play is divided to mark the change of time or place, and to give a respite to the actors and to the audience. In Greek plays there are no separate acts, the unities being strictly observed, and the action being continuous from beginning to end. If the principal actors left the stage the chorus took up the argument, and contributed an integral part of the play, though chiefly in the form of comment upon the action. When necessary, another drama, which is etymologically the same as an act, carried on the history to a later time or in a different place, and thus we have the Greek trilogies or groups of three dramas, in which the same characters reappear. The Roman poets first adopted the division into acts, and suspended the stage business in the intervals between them. Their number was usually five, and the rule was at last laid down by Horace in the Ars Poetica—

On the revival of letters this rule was almost universally observed by dramatists, and that there is an inherent convenience and fitness in the number five is evident from the fact that Shakespeare, who refused to be trammelled by merely arbitrary rules, adopts it in all his plays. Some critics have laid down rules as to the part each act should sustain in the development of the plot, but these are not essential, and are by no means universally recognized. In comedy the rule as to the number of acts has not been so strictly adhered to as in tragedy, a division into two acts or three acts being quite usual since the time of Molière, who first introduced it. It may be well to mention here Milton’s Samson Agonistes as a specimen in English literature of a dramatic work founded on a purely Greek model, in which, consequently, there is no division into acts.

For “acting,” as the art and theory of dramatic representation (or histrionics, from Lat. histrio, an actor), see the article.

ACTA DIURNA (Lat. acta, public acts or records; diurnius, daily, from dies), called also Acta Populi, Acta Publica and simply Acta or Diurna, in ancient Rome a sort of daily gazette, containing an officially authorized narrative of noteworthy events at Rome. Its contents were partly official (court news, decrees of the emperor, senate and magistrates), partly private (notices of births, marriages and deaths). Thus to some extent it filled the place of the modern (q.v.). The origin of the Acta is attributed to Julius Caesar, who first ordered the keeping and publishing of the acts of the people by public officers (59 ; Suetonius, Caesar, 20). The Acta were drawn up from day to day, and exposed in a public place on a whitened board (see ). After remaining there for a reasonable time they were taken down and preserved with other public documents, so that they might be available for purposes of research. The Acta differed from the Annals (which were discontinued in 133 ) in that only the greater and more important matters were given in the latter, while in the former things of less note were recorded. Their publication continued till the transference of the seat of the empire to Constantinople. There are no genuine fragments extant.

ACTAEON, son of Aristaeus and Autonoë, a famous Theban hero and hunter, trained by the centaur Cheiron. According to the story told by Ovid (Metam. iii. 131; see also Apollod iii. 4), having accidentally seen Artemis (Diana) on Mount Cithaeron while she was bathing, he was changed by her into a stag, and pursued and killed by his fifty hounds. His statue was often set up on rocks and mountains as a protection against excessive heat. The myth itself probably represents the destruction of vegetation during the fifty dog-days. Aeschylus and other tragic poets made use of the story, which was a favourite subject in ancient works of art. There is a well-known small marble group in the British Museum illustrative of the story.

ACTA SENATUS, or, minutes of the discussions and decisions of the Roman senate. Before the first consulship of Julius Caesar (59 ), minutes of the proceedings of the senate were written and occasionally published, but unofficially; Caesar, desiring to tear away the veil of mystery which gave an unreal importance to the senate’s deliberations, first ordered them to be recorded and issued authoritatively. The keeping of them was continued by Augustus, but their publication was forbidden (Suetonius, Augustus, 36). A young senator (ab actis senatus) was chosen to draw up these Acta, which were kept in the imperial archives and public libraries (Tacitus, Ann. v. 4). Special permission from the city praefect was necessary in order to examine them. For authorities see.

ACTINOMETER (Gr. , ray,  , measure), an instrument for measuring the heating and chemical effects of light. The name was first given by Sir John Herschel to an apparatus for measuring the heating effect of solar rays (Edin. Journ. Science, 1825); Herschel’s instrument has since been discarded in favour of the pyrheliometer (Gr. , fire,  , sun). (See .) The word actinometer is now usually applied to instruments for measuring the actinic or chemical effect of luminous rays; their action generally depends upon photochemical changes (see ). Certain practical forms are described in the article.

ACTINOMYCOSIS, a chronic infective disease occurring in both cattle and man. In both these groups it presents the same clinical course, being characterized by chronic inflammation with the formation of granulomatous tumours, which tend to undergo suppuration, fibrosis or calcification. It used to be believed that this disease was caused by a single vegetable parasite, the Ray-Fungus, but there is now an overwhelming mass of observations to show that the clinical features may be produced by a number of different species of parasites, for which the generic name Streptothrix has been generally adopted. In 1899 the committee of the Pathological Society of London recommended that the term Streptotrichosis should be used as the appropriate clinical epithet of the large class of Streptothrix infections. And since that year the name Actinomycosis has been falling into disuse, and in any case is only used synonymously with Streitotrichosis. For a further account of these parasites see the articles on and on.

Pathological Anatomy.—The naked-eye appearance of the different organs affected by Streptothrix infection varies according to the duration and acuteness of the disease. In some tissues the appearance is that of simple inflammation, whereas in others it may be characteristic. The liver when affected shows scattered foci of suppuration, which may become aggregated into spheroidal masses, surrounded by a zone of inflammation. In the lungs the changes may be any that are produced by the following conditions. (1) An acute bronchitis. (2) A phthisical lung, grey nodules being scattered here and there almost exactly simulating tuberculous nodules. (3) An acute broncho-pneumonia with some interstitial fibrosis and a tendency to abscess formation. The most characteristic lesions are