Metal reproductions of classic outdoor thermometers are hotter than ever. From famous makers of agricultural equipment to thermometers that feature Hollywood film stars. In addition to classic metal reproductions, outdoor thermometers come in many other shapes and sizes. Artists and designers have come up with an almost endless variety of fun themes.

More then just a simple, tried and true way to tell the temperature, thermometers can be ornamental too. Outdoor thermometers can be functional as well as decorative. The thermometers we are used to seeing are referred to as mercury in glass. The mercury in glass thermometer was invented by Dr. Daniel Fahrenheit. If that name sounds familiar, it should. Dr. Fahrenheit also developed the temperature scale of the same name.

The mercury in glass thermometer is a primary thermometer, since there is no need for it to be calibrated against a known value. The thin glass tube or capillary contains a small amount of mercury in a reservoir referred to as a bulb. The mercury often has been tinted red to make the thermometer easier to read. The tube or capillary either is filled with an inert gas like nitrogen or is drawn to create a vacuum. As the ambient temperature rises, the mercury expands and rises in the tube.

The principle behind the mercury in glass thermometer is simple. As the ambient temperature rises, the mercury expands and rises from the bulb through the capillary.

The scale of the thermometer is spaced accordingly. Even though Dr, Fahrenheit invented the mercury in bulb thermometer, the same system can be used to measure in the Celsius scale. The Celsius scale is the invention of Anders Celsius. Anders Celsius had originally thought of the thermal scale as an inverse of the Fahrenheit scale. The boiling point of water would be represented as zero and the freezing point of water would be represented by 100.

In seventeen forty four, Celsius developed the final version of his temperature scale. The freezing point of water, or thirty two degrees Fahrenheit, would be zero. The boiling point of water, or two hundred and twelve degrees Fahrenheit, would be represented by one hundred. The remaining length of the scale would be divided into increments of one hundred. Many household thermometers display both temperature scales.

Mercury is a toxic substance and you should avoid exposure to mercury, either by contact with the skin or inhaling vapors emitted by uncontained mercury. Most household thermometers contain a very small amount of mercury and breaking your outdoor thermometer does not generally pose a health hazard.

Like metal and tin signs, outdoor thermometers have been used for many years as a marketing device. Companies wishing to advertise their goods and services would give away outdoor thermometers to retailers and shopkeepers. Shopkeepers would in turn hang them outside their shops. Like antique metal and tin signs, many of these advertising thermometers have gone on to become quite collectible.

Decorative outdoor thermometers are a great way to accent your patio and porch furniture. Nautical decor designs are popular and the thermometer is often combined with a barometer and humidity gauge. Birdhouses, garden gnomes, weather vanes and many other designs can brighten your yard or patio.

A good spot to place your outdoor thermometer is in the shade. This is true whether you have a mercury in glass thermometer or a dial model. A thermometer exposed to direct sunlight will read higher than the actual ambient temperature. The glass metal or other materials will absorb heat from the sun, causing the mercury to rise beyond the actual air temperature.

Dial thermometers operate on a different principle than the mercury type. Dial thermometers rely on a bimetal coil. Similar to a thermocouple, the metals expand and contract in reaction to changes in temperature. The dial provides designers with a different palette, offering very distinctive and decorative possibilities.