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"Leslie's hygrometer, which is an adaptation of his differential thermometer, is formed by uniting two tubes having a ball blown on the end of each, into which some colored sulphuric ether has been previously introduced. When both bulbs are at the same temperature, the fluid stands at the zero of the scale, but when one of them is covered with wetted paper the instrument shows the depression of temperature of the wetted bulb." — Encyclopedia Britannica, 1893

Leslies Hygrometer

"Leslie's hygrometer, which is an adaptation of his differential thermometer, is formed by uniting two…