Radiometer (also called the radio mill) is a device for measuring intensity electromagnetic radiation. However this bulb radiometer was invented in 1873 Mr Crooke while he was working doing research on an element called Thallium. So this instrument like many other scientific discoveries was done inadvertently. The radiometer is made from a glass bulb from which much of the air has been removed to create a partial vacuum. Pressure inside is few hundred times less. Inside the bulb ona spoke and spinde is a

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