What to Know About Collectible Thermometers

Collectible mercury thermometers on eBay come in many shapes, sizes, and transduction methods. The basic concept of each different type of thermometer is the same, but the style differs.

Broad categories of reasonably priced thermometers

There are four broad categories of thermometers to be aware of:

  • Clinical: Clinical thermometers are thermometers that were designed for clinical use. These are the thermometers that are used to take a person's temperature through one of three different means. Since clinical thermometers are used to take the temperature of a person, they tend to be sized uniformly and appropriately for human use.
  • Advertising: Advertising thermometers are thermometers that have some sort of advertisement or marketing associated with it. These thermometers are used for other than clinical applications such as measuring the ambient temperature of a local environment.
  • Galileo: Galileo thermometers are a series of fluid-filled orbs in a cylindrical tube that has water in it. Galileo thermometers are not used clinically but only for monitoring local environmental changes in air temperature.
  • Decorative: Decorative thermometers are designed specifically to be aesthetically pleasing. Decorative thermometers incorporate a standard weather thermometer into a decorative piece. In this category of vintage thermometers, the thermometer can be the focal point of the piece or it can simply accent the larger piece that it is incorporated into.
Does the fluid in the thermometer matter?

The fluid in the thermometers has certain physical characteristics that make it ideal for different areas. The alcohol-based red fluid that is often found in many thermometers will actually freeze at a lower relevant temperature than mercury does, making it more functional at lower temperatures. Furthermore, the alcohol-based red fluid is much less toxic than its mercury counterparts if the thermometer was to break. The mercury-based thermometers were not invented until the early 1900s. Therefore, you won't find vintage glass mercury thermometers manufactured before that date.

Other considerations regarding vintage thermometers

Vintage thermometers can be hung on the wall or placed on a desk. Their placement will often define their shape, as thermometers meant for desk placement tend to be larger and more box-like. Alternatively, thermometers meant for wall placement tend to be slimmer and shallower. Advertising thermometers are often the most variable in terms of shape and size due to their dual purpose. One of the purposes of an advertising thermometer is to provide the user with the temperature while an equally important function is marketing for a particular product or brand.