The thermoscopes were the first instruments used to measure the temperature of things. It was started as a glass bulb on top of a tube coming out of a container of colored water. Liquid would rise or fall when the air around it would grow warmer or cooler. Engraved marks on the tube made for the scale.
In 1691 the first sealed thermometer was invented. It sealed alcohol in glass, and had 50 " degree " marks. Yet it had no fixed points. These thermometers were often called "spirit" thermometers. I have no clue why.
Gabriel Fahrenheit started using mercury as the liquid instead of dye or colored water. Mercury was a good liquid to use for many reasons. First of all, the thermal expansion of mercury is pretty uniform. It also does not stick to glass, and it stays as a liquid over almost any temperature. It's also very easy to read because of it's appearance.
