"1. Fire... throws out light, heat, and smoke (or fume.) The [first] two... move in right lines, and with great swiftness; the latter is but just separated from the fuel, and then moves only as it is carried by the stream of rarefied air; and without a continual accession and recession of air, to carry off the smoky fumes, they would remain crowded about the fire, and stifle it."