Antique thermometers are a fascinating and often very collectible item that can be found in a variety of styles, material, and construction. Many of these old thermometers are encased in glass, but some have been designed to look like a metal clock or soda bottle, while others have intricate lettering or decorative borders. They are also usually quite expensive and very rare.

The invention of the antique thermometers was a crucial step in the Scientific Revolution, and it would not have been possible without an accurate way to measure temperature. Thermometers use a system of expansion and contraction to read the temperature, and they are used by scientists in a number of fields including biology, medicine, and chemistry. Early thermometers were air-based, but the problem was that the different expansions of different gases could confuse readings. The first solution was a liquid thermometer, and in the mid-17th century this was perfected. The most famous example of this is Galileo’s thermometer, but there were other versions as well, such as the one made by the Grand Duke of Tuscany, Santorio Santorio in 1612.

These early thermometers were not very accurate, and even the best ones had errors of a few degrees Fahrenheit. But by the 1800s, advancements in technology and manufacturing were making thermometers much more reliable. Thermometers had to be able to measure high temperatures, and that meant they needed to be a bit larger than the earlier air-based instruments. This led to the design of a liquid-in-glass thermometer, which could be used to take readings for a range of temperatures.

Another key development in the history of thermometers was the reversal of the Celsius scale, putting zero at freezing rather than boiling. Various people are credited with this innovation, including Linnaeus, the founder of modern taxonomy; the physicist and alchemist Robert Boyle; and the Swedish instrument-maker Ekstrom. The reversal was finalized in 1749, and it was from this point that thermometers were commonly read in the centigrade scale.

Another type of antique thermometer is the advertising thermometer, which was used by businesses as a form of marketing and promotion. These were often made from metals such as tin and wood, and they would be hung on a wall or in a window. They were often decorated with the company name or logo and artistic elements that were popular in the period they were made. This might include swirls or floral designs, or it could simply be lettering or images associated with the business in question. These advertising thermometers can be very desirable, and they can sell for thousands of dollars at auction or at 1stDibs. They are often very expensive and rare, and they can also be difficult to find. This means that they can be a great investment for the collector.