Meteorology known as the first "anemometer". In 1607, Galileo Galilei constructed a thermoscope. In 1611, Johannes Kepler wrote the first scientific treatise on snow crystals: "Strena Seu de Nive Sexangula (A New Year's Gift of Hexagonal Snow)". In 1643, Evangelista Torricelli invented the mercury barometer. In 1662, Sir Christopher Wren invented the mechanical, self-emptying, tipping bucket rain gauge. In 1714, Gabriel Fahrenheit created a reliable scale for measuring temperature with a mercury-type thermometer. In 1742, Anders Celsius, a Swedish astronomer, proposed the "centigrade" temperature scale, the predecessor of the current Celsius scale. In 1783, the first hair hygrometer was demonstrated by
Kodaikanal mercury poisoning in Kodaikanal originated at a thermometer factory that was owned by Hindustan Unilever. Unilever acquired the thermometer factory from cosmetics maker Pond's India Ltd. Pond's moved the factory from the United States to India in 1982 after the plant owned there by its parent, Chesebrough-Pond's, had to be dismantled following increased awareness in developed countries of polluting industries. In 1987, Pond's India and the thermometer factory went to Hindustan Unilever when it acquired Cheseborough-Pond's globally. The factory imported mercury from the United States, and exported finished thermometers to markets in the United States and Europe. Around 2001, a number of