A typical Liquid-In-Glass Thermometer takes advantage of the fact that most substances expand when heated. When the temperature rises, a liquid sealed inside the glass tube of the thermometer expands from a bulb at the instrument's base and rises-up inside the tube. Temperature markings are made along the edge of the tube (the thermometer is calibrated to make sure the marks are accurately placed) and the temperature is read by matching the level of the liquid with the markings.
---David Murphy
