Note: Do not rely on this information. It is very old.
Cornish BoilerCornish Boiler, a cylindrical steam-boiler with a single flue passing from end to end. The diameter of the flue is usually three-fifths of the diameter of the boiler itself. The furnace is built in the front part of the flue; it is backed by a bridge of firebrick or of hollow metal, inside which the water may flow. Effective eddies are produced in the flow of the burning gases by corrugating the flue and by the use of Galloway tubes. These latter are hollow tubes joining opposite sides of the flue, thus permitting the water to flow across and so be heated. Besides increasing the heating surface, they strengthen the structure considerably.
Click for more about Galloway