ClipArt ETC
"A horizontal tubular, which is found to be extremely powerful as well as economical. It is a rectangular box 6 feet long, made of 2-inch iron pipes, fixed into hollow water spaces which form the ends; these pipes act as fire bars, and form the sides of the furnace. above the fire there are three series of horizontal pipes, each covered by a layer of tiles so placed as to convert the two intervening spaces into flues, along which the flames and smoke travel for 18 feet, the smoke escaping at the far end by an opening in the upper layer of tiles." — Encyclopedia Britannica, 1893

Ladds's Boiler

"A horizontal tubular, which is found to be extremely powerful as well as economical. It is a rectangular…