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17 October 2003

How to Make a Hygrometer

Adapted from A Thousand and One Formulas 1920 by Sidney Gernsback.

The hygrometer is an instrument to measure the degrees of dryness or mois-ture of the atmosphere. There are various kinds of hygrometers; for whatever body either shrinks or swells by dryness or moisture, is capable of being formed into an hygrometer, such as woods of most kinds, particularly ash, deal, poplar, etc. The following is the most lasting and con-venient mode of construction for an in-strument of this description.

Take a very fine balance, and place in it a sponge, or other body which easily absorbs moisture, and let it be in equilib-rium with a weight hung at the other end of the beam. If the air becomes moist, the sponge, becoming heavier, will prepon-derate; if dry, the sponge will be raised up.

This balance may be contrived in two ways, by either having the pin in the mid-dle of the beam, with a slender tongue, a foot and a half long, pointing to the di-visions of an arched plate, fitted on it, or the other extremity of the beam may be so long, as to describe a large arc on a board placed for the purpose.

To prepare the sponge, it may be neces-sary to wash it in water and, when dry, in water or vinegar, in which sal ammoniac or salt of tartar has been dissolved and Iet it dry again; then it is fit for use. The instrument can be hung against the wall; and, in that case a bit of steel, as at "A," (see figure) should be placed before the needle. to keep it straight.