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A SPIRAL THERMOMETER

Number in the past inventory 2897
Number in the current inventory 86

INSTRUMENT: A SPIRAL THERMOMETER

Age: beginning of the twentieth century

Creator: Abraham-Louis Breguet (1747-1823) (A famous watchmaker from Paris)

Materials: wood, glass, brass, velvet porcelain, iron, zinc, silver gold, platinum

Size: (205, Ø 165) mm

State of conservation: Good

Information: From the information contained in the old inventory register, found in the school, the instrument is said to have been added to the inventory with the number 2897 on 10th March 1924 priced at 480 liras.

Description: On a wooden circular base which rests on three wooden legs, two brass clamps are screwed; they hold up a curved scale, graduated from -10°C to 40°C, with sensitivity of one degree with a curved rod which supports with a clamp a metal spiral. At the lower end this spiral is inserted on a pin fixed to the base. The spiral consists of platinum, gold and silver placed one on top of the other in this order and they are passed to the rolling mill and heated up. To prevent breakage, the foil is fixed in such a way to have platinum on the outside as this metal has the lowest coefficient of expansion, followed by gold with a medium coefficient and by silver with the highest coefficient. The spiral is connected to a pointer (recently substituted) free to rotate. The curved scale and the pin are connected to the bottom of the base to two metal small bars which hold two brass terminal clamps. On the base there is a groove filled with a velvet string on which a glass bell and a porcelain plate are placed; on the outside on the plate these words are written: “Metallthermometer nach Breguet. Gesetzl: geschützt”.

Use: The thermometer operates according to differential expansion of three metals forming the spiral which expands due to the effect of the heat or thermoelectric heat (connecting the terminals to a generator) and acts on the pointer. The presence of the bell allows a more reliable and precise measurement of the temperature.

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