Small "Field" Boiler Tube complete

Small "Field" Boiler Tube complete, fixed in portion of tube plate

This is an example of the double water tube for steam boilers, patented in 1862, by Mr. E. Field and Messrs. M. and R. M. Merryweather. By them it was applied to the boilers of steam fire-engines, in which lightness and rapid steaming are of great importance. This was the first practical application of an internal tube within a heated one for separating the currents of hot and cold water from one another.