A method is described by which the humidity of the air in very small spaces can be measured. Paper is a hygroscopic substance which absorbs an amount of water from the air proportional to the relative humidity. Using a torsion balance, it is possible to measure the change in weight of a piece of paper which weighs about 10 mg. with sufficient accuracy to measure the relative humidity of the air to 2 per cent.
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Kenneth Mellanby (1933) studied this question.
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