ABSTRACT
The meteorological instruments in use during the eighteenth century were the rain-gauge, for measuring the amount of rain-fall; the thermometer, for measuring degrees of temperature; the barometer, for measuring variations of atmospheric pressure and the heights of mountains. The story of the improvements in the instruments is so intimately connected with De Luc’s meteorological researches as to be almost inseparable from them. It is unnecessary to add anything about the barometer; but something must be said about the more familiar types of thermometer before proceeding to give an account of the anemometers and hygrometers in use during the eighteenth century. The chief point in the concluding Essay, on the meteorological applications of hygrometry, is De Saussure’s attempt to disprove De Luc’s hypothesis that the barometer falls when the atmospheric air becomes lighter, bulk for bulk, in consequence of the admixture of water-vapour.
