Pictet's experiment is the demonstration of the reflection of heat and the apparent reflection of cold in a series of experiments performed in 1790 (reported in English in 1791 in An Essay on Fire) by Marc-Auguste Pictet —ten years before the discovery of infrared heating of the Earth by the Sun. The apparatus for most of the experiments used two concave mirrors facing one another at a distance. An object placed at the focus of one mirror would have heat and light reflected by the mirror and focused. An object at the focus of the counterpart mirror would do the same. Placing a hot object at one focus and a thermometer at the other would register an increase in temperature on the thermometer. This was sometimes demonstrated with the explosion of a flammable mix of gasses in a blackened balloon, as described and depicted by John Tyndall in 1863.