Anders Celsius's temperature scale
Anders Celsius defined his temperature scale on the melting and boiling temperature of water in 1841. Although Celsius did not discover the thermometer – both Philo and Hero of Alexandria (who also mentioned steam power in 50 BC) described such a principle – his design was much more precise than any previous such invention. Celsius scaled his measurements as 0 for boiling point and 100 for freezing point but the order was later reversed. You might have been told that water boils at 100 degrees Celsius (212F) but the boiling point of water actually depends on the oxygen content and atmospheric pressure. The higher the altitude, the lower the temperature at which water boils. People who live at high altitudes, like Tibetans, drink their tea while it is bubbling with boiling. Many Tibetans who moved to India suffered serious burns when they drank their boiling tea at sea-level. British Standard 6008 and International Standard ISO 3103 advise that tea is best made with water that is freshly boiled. Prolonged boiling of water, or water that is boiled twice, drives off the dissolved oxygen in the water, making the tea taste flat.