Sonomètre of Loulié

The records of the Academy (Procès verbaux) for that day read: Loulié invented both a table-top and a portable model of the sonomètre.

The first component is an instrument string (shown in red on the modified engravings) that is strung from one end to the other of a shallow rectangular wooden box.

The second component consists of one or more movable pieces of wood (shown in yellow on the engravings) that are marked to represent the 11 notes of the musical scale.

Pulling out this graduated strip of wood causes the inner end of the movable piece to rest on the string, shortening or lengthening its length so that the desired pitch will be sounded.

The original illustration of this table-top device included the "proportions" of an "exact division of the notes" into the larger or smaller intervals characteristic of the unequal temperament preferred by Loulié.