Before thermometers were invented no one could be very exact about temperature.
As far back as the ancient Greeks, the principle that some substances, like air, expand as they get hotter and contract when they get cooler, had been observed, but it took a long time before this theory was successfully applied to the production of a device that could measure temperature.
Freezing and Boiling. In 1592 Galileo Galilei produced a thermoscope, like a thermometer but without a scale, so it wasn’t very accurate. His contemporary, an Italian doctor called Santorio, is believed to have been the first to add a numerical scale.
In the 1680s Guillaume Amontons developed a thermometer that used mercury, which expands as it gets hotter (earlier ones used air, which isn’t as effective). But Amontons’ thermometer still wasn’t very good.
Gabriel Fahrenheit made a big difference to the development of the invention when he made the first successful mercury thermometer in 1714. Ten years later he came up with a temperature scale that’s still used widely today.
Although Fahrenheit is still used in the USA, most people use centigrade (or Celsius) for measuring temperature. Centigrade is a lot more sensible: Swedish astronomer Anders Celsius came up with the scale in 1742 based on the freezing point and boiling point of water (0 degrees centigrade and 100 degrees centigrade respectively, though originally it was the other way around). Fahrenheit chose 32 degrees as the freezing point of water and 212 as the boiling point, perhaps he just liked to make things complicated.
MAKE YOUR OWN THERMOMETER
A thermometer is a really clever piece of kit. It’s hard to replicate such an accurate device, but here is a way to create a very basic one. Build one to earn your star.
WHAT YOU NEED
water, a clear plastic bottle with lid, a clear plastic drinking straw,
food coloring, Blu-tack
WHAT TO DO
Chill a bowl of water in the fridge overnight. Fill a clear plastic bottle right to the top with the tap water
(1). Add a few drops of food coloring to the water to make the temperature change easily visible. Cut a hole in the top of the bottle lid wide enough for the straw to fit through
(2). Push the straw into the bottle through the hole but don’t let it touch the base of the bottle. Take the Blu-tack and use it to seal the gaps between the straw and the bottle top
(3). As the cold tap water in the bottle rises to room temperature, so the water should rise up the straw. Mark the new level on the straw
(4). Place your thermometer in the bowl of cold water you kept in the fridge. Leave it to stand for 30 mins and watch as the water level falls
(5). Then place your device in the sink with hot water and watch as the water level rises
(6). The Kelvin temperature scale was developed in the 1880s by Lord Kelvin and is used for extremes of temperature. 0 degrees in the Kelvin scale is absolute zero – the coldest anything can get – and is equivalent to minus 273 degrees centigrade.