Thermometers can be very simple instruments, based on the expansion or contraction of mercury or colored alcohol in a sealed tube. But thermometers can also be more complicated - for example, some digital thermometers rely on changes in electrical resistance to measure temperature.

Now a new type of thermometer has really gone high-tech, but in doing so have returned to the original principle of a liquid in a tube. Except now the tube is a hollow cylinder made out of carbon atoms, and the cylinder is only about 1/1000th the width of a human hair. The liquid used in these so-called "nanothermometers" is the element gallium, a metal which, like mercury, can remain a liquid at room temperatures.

Thermometers this small will be useful for taking measurements in microscopic environments, and they work at temperatures ranging from around 100 to 1000^oF. But it will take a high-powered scanning electron microscope to actually read the level of gallium in the tube.