Galileo's thermometer measured heat by observing the changes in the density of water in glass-filled bulbs. This method of liquid in a sealed glass bulb or tube was used to design and develop a number of old-fashioned instruments that work on the principle of the changes in water when heated and cooled to measure temperature changes.
The barometer, an instrument for measuring air pressure, was invented by Italian mathematician and physicist Evangelista Torricelli in 1643. Using observation of how a siphon works, Torricelli used a mercury-filled tube to determine atmospheric pressure at sea level.
Water-absorbing properties of hair were used in 1783 to develop the first hygrometer, an instrument for measuring humidity. This old-fashioned hygrometer was calibrated by first determining the length of a hair at total dehydration and at total saturation, or 0 percent humidity and 100 percent humidity, respectively. Relative humidity then could be calculated by using these two set points.
Leone Battista Alberti (1404-1472) is credited with inventing the first useful anemometer, an instrument to measure wind speed.
Irish astronomer Thomas Romney Robinson developed the rotating-cup anemometer that is still used in small weather stations.
As an instrument for measuring humidity, the sling psychrometer came into use during the 19th century.
This old-fashioned weather instrument used two identical mercury thermometers mounted on a wooden paddle. The bulb of one of the thermometers is wrapped in wet absorbent materials. A person then whirls (slings) the handle around through the air and the thermometer with the wet bulb cools rapidly compared to the other due to evaporation properties of water. The temperature difference between the two thermometers can then be converted to relative humidity.