been confirmed, extended in a variety of ways, or explained on the principles of improved chemistry, by Dr. Percival and Mr. Henry in England, Dr. Woodhouse in America, and M. Sennebier and M. Théodore de Saussure, as well as various other philosophers, on the continent of Europe. It is agreed that in the day-time plants imbibe from the atmosphere carbonic acid gas, (which was formerly called fixed air, and is an union of oxygen and carbon), that they decompose it, absorb the carbon as matter of nourishment which is added to the sap, and emit the oxygen. So they absorb the same gas from water, when it is separated from that fluid by the action of light. The burning of a candle, or the breathing of animals, in confined air, produces so much of this gas, that neither of these operations can go on beyond a certain time, but the air so contaminated serves as food for vegetables, whose leaves, assisted by light, soon restore the oxygen, or, in other words, purify the air again. This beautiful discovery, for the main principles of which we are indebted to the celebrated Dr. Priestley, shows a mutual depend-
