Galileo's thermometer, the breakthrough invention.

As we know, the Italian Galileo Galilei was a great scientific inventor of the late 16th and early 17th century. He was also a mathematician, astronomer, physicist and philosopher. His greatest invention was the refracting telescope, whose object allowed him to observe the moon, Jupiter and the satellites orbiting around them. On several occasions he was banned by the church for his "daring" discoveries and books, as he was at the height of the Holy Inquisition.

It was Galileo who discovered that the density of a liquid varies with temperature. This discovery led him to create an instrument to measure the ambient temperature and thus the so-called Galilei thermometer was born.

Unlike the typical mercury thermometer, this one consists of a glass cylinder filled with alcohol in which small glass balls are suspended inside. These glass balls contain a coloured liquid (often alcohol) but can also be water with dye, simply to make them easier to identify, as these balls have a pendant on the bottom with the different temperature values. Each of these spheres has a different amount of liquid, so their density and buoyancy are different.

According to Galileo's principle, if the ambient temperature changes, the density of the alcohol changes and this is when the small spheres inside rearrange and float to a certain height according to their density. Generally, two groups of spheres are formed, one at the bottom and one at the top of the cylinder. If the ambient temperature rises, the upper spheres fall while the others are at the bottom. The temperature will always be marked by the sphere floating at the lowest height of the upper group of spheres. It is necessary to take into account its inaccuracy depending on the number of spheres and their values. For example, in the picture we can see that there are two thermometers in which there is no sphere at the top, this is because the value marked by the highest sphere is lower than the ambient temperature value at the moment when the picture was taken.

A very curious and interesting object but, with the passage of time and the advance of technology, it acquires a decorative rather than a functional use. Nowadays we can find out what the ambient temperature is with a simple click on our electronic devices, such as mobile phones, computers, tablets and even smart watches.