Tub′u-lar Boil′er.
（Steam.) A name properly applicable to a steam-boiler in which the water circulates in pipes, vertical, horizontal, or inclined, the fire encircling them. See tubular steam-boiler; Tubulous boiler. When the fire passes through the tubes, they are properly flues. The term is, however, applied to pipes, whether water-tubes or fire-tubes, below a certain diameter; the term flues belonging to those of a relatively larger diameter. See steam-boiler, Plate LXI., in which are numerous illustrations of each kind; also locomotive, page 1346; and other places noted in the list under steam-engine.
