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Gay-Lussac’s earlier researches were mostly physical in character and referred mainly to the properties of gases, vapour-tensions, hygrometry, capillarity, &c.

The dew-point method is indeed in some ways a fundamental method of hygrometry.

So that, to get materials for further advance, astronomy requires not only the indirect aid of the sciences which have presided over the making of its improved instruments, but the direct aid of an advanced optics, of barology, of thermology, of hygrometry; and if we remember that these delicate observations are in some cases registered electrically, and that they are further corrected for the "personal equation"—the time elapsing between seeing and registering, which varies with different observers—we may even add electricity and psychology.

The Royal Irish Academy in Dublin have published a report of their proceedings, which comprise reports on rain-falls, meteors, ancient urns, and other Irish antiquities, besides Roman and Carthaginian; on hygrometry, chiefly with regard to the pressure of the dew-point; and on artificial islands.

Hygrometry, 332, 333; hygrometric wind-rose, 333.