Cagniard de la Tour-type siren
Date: 1870-1890
Inventory Number: DW0351
Classification: Siren
Subject:
Maker: E. Ducretet & Cie (1864 - 1931)
Cultural Region:
Place of Origin:
Dimensions:
23.5 x 11 x 11 cm (9 1/4 x 4 5/16 x 4 5/16 in.)
Bibliography:
Elementary Treatis on Physics: Experimental and Applied for the Use of Colleges and Schools. Translated and Edited from Ganot's Éléments de Physique
Catalogue des instruments de précision de E. Ducretet & Cie
Description:
The siren sits on top of a removable weighted turned mahogany base. The bottom of the siren is made of a cylindrical cavity in which air is continuously pushed in. This pressurized air comes from under the cavity, most likely from a wind chest and bellows (or soufflerie).
On top of the cavity is a fixed plate with 16 small holes. On top of that plate is a rotating plate with an identical number of holes. This plate turns owing to a (now missing) small grooved wheel attached to the central rod, which was linked to a larger mechanical wheel. The number of turns is displayed by two dials: the one on the right (marked "100") showing units from 0 to 100 and the one from the left (marked "2500") divided in units from 0 to 25. The small screws at the back give access to the dials' mechanism, so that either wheel can be uncoupled from the endless screw making them turn. The upper thumb screw is used to adjust the height of the rotating plate.
On top of the cavity is a fixed plate with 16 small holes. On top of that plate is a rotating plate with an identical number of holes. This plate turns owing to a (now missing) small grooved wheel attached to the central rod, which was linked to a larger mechanical wheel. The number of turns is displayed by two dials: the one on the right (marked "100") showing units from 0 to 100 and the one from the left (marked "2500") divided in units from 0 to 25. The small screws at the back give access to the dials' mechanism, so that either wheel can be uncoupled from the endless screw making them turn. The upper thumb screw is used to adjust the height of the rotating plate.
In Collection(s)
Signedon front: E. Ducretet et Cie / A PARIS
FunctionThis instrument was used to measure the number of vibrations of a body in a given time.
Here is the description given by Ganot: "For the sake of simplicity, let us first suppose that in the moveable disk A there are eighteen holes, and in the fixed plate B only one, which faces one of the upper holes. The wind from the bellows striking against the sides of the latter, the moveable disc begins to rotate, and the space between two of its consecutive holes closes the hole in the lower plate. But as the disc continues to turn from its acquired velocity two holes are again opposite each other, a new impulse is produced, and so on. During a complete revolution of the disc the lower hole is eighteen times open and eighteen times closed. A series of effluxes and stoppages is thus produced, which makes the air vibrate, and ultimately produces a sound when the successive impulses are sufficiently rapid. If the fixed plate, like the moving disc, has eighteen holes, each hole would separately produce the same effect as a single one, the sound would be eighteen times as intense, but the number of vibrations would not be increased." [...]
"Since the sound rises in proportion to the velocity of the disc A, the wind is forced until the desired sound is produced. The same current is kept up for a certain time, two minutes for example, and the number of turns read off. This number multiplied by 18, and divided by 120, indicates the number of vibrations in a second."
Here is the description given by Ganot: "For the sake of simplicity, let us first suppose that in the moveable disk A there are eighteen holes, and in the fixed plate B only one, which faces one of the upper holes. The wind from the bellows striking against the sides of the latter, the moveable disc begins to rotate, and the space between two of its consecutive holes closes the hole in the lower plate. But as the disc continues to turn from its acquired velocity two holes are again opposite each other, a new impulse is produced, and so on. During a complete revolution of the disc the lower hole is eighteen times open and eighteen times closed. A series of effluxes and stoppages is thus produced, which makes the air vibrate, and ultimately produces a sound when the successive impulses are sufficiently rapid. If the fixed plate, like the moving disc, has eighteen holes, each hole would separately produce the same effect as a single one, the sound would be eighteen times as intense, but the number of vibrations would not be increased." [...]
"Since the sound rises in proportion to the velocity of the disc A, the wind is forced until the desired sound is produced. The same current is kept up for a certain time, two minutes for example, and the number of turns read off. This number multiplied by 18, and divided by 120, indicates the number of vibrations in a second."
Primary SourcesE. Ducretet et Cie, Petit catalogue des instruments de précision de E. Ducretet et Cie (élève de M. Froment) (Paris, 1880), part 2, 167, no. 1652.