Last minute

Ever had an evening when you arrive home at 11.50pm and don't have a photo.

Grabbed the first thing that came to hand! This is a section of a Galileo thermometer.

Although Galileo did invent what was known as a thermoscope or air thermometer, it was a group of academics, some fifty years later, which included one of his pupils, who invented the principle of what should be called a slow or lazy thermometer. This was the mid 15th century.

The Natural History Museum in London reinvented the design and began to sell them in the 1990's. They named them after Galileo as it was he who discovered that the density of a liquid changes in proportion to its temperature, which is the principle on which this thermometer is based.

A number of liquid filled bulbs, coloured only for effect, have weights attached which alter the buoyancy at determinate temperatures as they float in a solution of ethanol and water. The bulb which floats nearest the centre or is in the centre of a group will show the ambient temperature.

With only 5 bulbs ranging between 18 and 26 degrees, I wouldn't like to use mine to make any serious recordings, but the principle was as accurate as measurements could be 550 years ago.

Amazing, they still sell today!