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Galileo's thermometer: how it works

Galileo's thermometer: how it works


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Galileo's thermometer: how the Galilean thermometer works and how it was built. Operating principles and useful information.

Modern meteorology has its roots in 1500 when the first ancestral form ofthermometer. In fact, Galileo did not invent what we commonly call "Galilean thermometer”But something that sees aoperationvery similar: Galileo's thermoscope.

Galileo's thermoscope

Similar toGalilean thermometerand theGalileo's thermoscope. If the origins of Galileo's thermometer are uncertain, those of his thermoscope are not. In the thermoscope, the water acts as an indicator and the thermal expansion is induced by the air. Thethermoscope it consists of a glass vial, slightly larger than an egg, the vial is characterized by a very long and thin neck.

How does it work?

The ampoule, held in the hands and partially immersed in water (in an inverted position), records a phenomenon of heat exchange:how does it work? When the heat from your hands is removed from the jug, the air inside cools and hisvolume decreases and this determines the rise of the water along the narrow neck of the ampoule. If you return to heat the jug with your hands, the volume of air increases and causes the water to descend along the neck. It is a sort of very rudimentary thermometer but which opens the doors to meteorology as a science.

TheGalileo's thermoscopeit had the sole function of "measuring cold and heat" and was the first ancestral sketch of a thermometer. Thethermoscope highlights the variations of theair densityproduced by temperature changes. With the inclusion of detailedgraduated scales, the thermoscope is transformed into the ampoule thermometer.

On the model ofGalileo's thermoscope the alcohol thermometer was developed, the one that today everyone knows asgalileo's thermometer.

Galilean thermometer

What we call "Galileo's thermometer" it's aalcohol thermometerand was developed by the pupils of Galileo Galilei by the scholars of the Accademia del Cimento, a Florentine school dated 1657. For its origins and itsoperation, theGalilean thermometerit is also said "Florentine alcohol thermometer ".

Galileo's thermometer was originally born with different graduated scales and with different measures: the consequence? The instruments were not calibrated / standardized, so the measurements they returned could not be compared. THEGalileo's thermometersthat we find on the market today, have been calibrated using standardized measurements that have become established later in the centuries.

Only in 1700, in fact, themercuryentered the scene along with numerous different thermometric scales. Among which the two thermometric scales currently used were most successful: the Celsius scale (Ourdegrees centigrade when we cook a dish in the oven or when we see the temperature of the fever!)and the ladder Fahrenheit, more used in the USA.

Mercury was going to replace the alcohol ofGalileo's thermometer and this time the ampoule with the graduated neck was much simpler. As fixed points of the scales, the temperature of the melting ice and the boiling temperature of the water were chosen.

Galileo's thermometer: how it works

As stated, theoperationbasic is very similar to that described for theGalileo's thermoscope. TheFlorentine alcohol thermometerit consists of a vertical glass cylinder, filled with alcohol in which some are suspendedflasks. A temperature is indicated on each bottle.

The bottles are filled, in turn, with a colored liquid so as to be identified based on the temperature. The bottles fluctuate in alcohol always due to the principle of thermal expansion. In a situation of thermal equilibrium, the temperature can be detectedobservingthe lower bottles among those placed in the upper part of the ampoule.

In conditions of thermal equilibrium, in fact, two groups of flasks are formed: the first placed in the upper part of the column and the second placed in the lower part of the column.

The functioning of Galileo's thermometer exploits the principle of Archimedes. From a physical point of view, in fact, if we have two bodies (or fluids) of different densities, the one with the lowest density will tend to rise upwards while the one with the highest density will tend to go downwards.

Also in this case, therefore, just like in the thermoscope, theGalilean thermometer highlights the variations of thedensity produced by temperature changes.

Where to buy it?

On "this Amazon page" there are several models. An advice? If you buy a small Galileo thermometer (within 30 cm) do not go beyond the 5-6 internal cruets, if you buy a large one (over 30 cm), buy one with 7-10 cruets. In this way you will be able to have more or less precise temperature measurements.


Video: Galileo Thermometer Experiment (May 2022).