It is interesting to follow the change of weather, day and night, summer and winter. You can watch the approaching storm, to notice the change in the shape of clouds. But much more can and measure the amount of precipitation that falls on a certain area, the wind speed during the storm, the amount of atmospheric pressure before and after the storm. For that meteorologists use of special devices.
Almost all substances expand when heated and contract when cooled. It is especially noticeable on the volume change of the liquid metal mercury. Hollow glass ball, to which is soldered a transparent tube filled with mercury. (Caution! Mercury is very poisonous!) This is the main element of the thermometer, which is well known to you - during the illness they measure the temperature. When heated, the mercury in the bulb expands and rises in the tube to which is attached a graduated scale. Upon cooling, the mercury level in the tube falls.
In Europe it is customary to measure the temperature in degrees Celsius". This system is based on the physical properties of water: at zero degrees, it turns into a solid state - freezes at 100° C in a gas.