Arca Musarithmica

The Arca Musarithmica (also Arca Musurgia or Musical Ark) is an information device that was invented by Jesuit scholar Athanasius Kircher in the mid 17th century. Its purpose was to enable non musicians to compose church music. Through simple combinatoric techniques it is capable of producing millions of pieces of 4-part polyphonic music. Like other calculating aids of the period, the Arca prefigures modern computing technology. It is among the earliest examples of "Artificial Creativity". The device anticipates aleatoric and computer compositional techniques of the 20th century (such as the "chance music" of John Cage), and can be thought of as a kind of music composition algorithm in physical form.

Mechanical music-making is nothing more than a particular system invented by us whereby anyone, even the ἀμουσος [unmusical] may, through various applications of compositional instruments compose melodies according to a desired style. We shall briefly relate how this mechanical music-making is done and, lest we waste time with prefatory remarks, we shall begin with the construction of the Musarithmic Ark.

The arca is a box containing a set of wooden rods or slats (or "tariffa" as Kircher called them). Each slat contains a set of numbers, which correspond to notes in a scale or mode, as well as an assortment of rhythmic treatments for those notes.

There are different sets of slats which contain musical phrases expressed in a variety of poetic meters (“Euripedaean”, “Anancreonic”, “Archilochan”, “Sapphic” and so on). Some of the rods are used for counterpoint in the "simple style" (or first-species counterpoint) in which all 4 parts have the same rhythm, and others are used for what Kircher calls the "florid style" (or fifth-species counterpoint), in which the 4 voices move independently.

Kircher first described the Arca in his book "Musurgia Universalis" (1650). Book 8 of this work (Musurgia Mirifica) is a longer treatise on using combinatoric techniques to construct music. Like the previous writings of Marin Mersenne, this work utilizes the ideas of Ramon Llull to show how a small amount of musical material can be combined to produce a prodigious number of melodies. Kircher goes on to describe the Arca itself, which employs this technique, and includes a fold-out illustration of the device, as well as a tables indicating the content of all the rods contained inside.

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