Probably one of the first sectional boilers brought into practical use
is one made of hollow cast iron spheres, each 8 inches in diameter,
externally, and 3/8 of an inch thick, connected by curved necks 3-1/2
inches in diameter. These spheres are held together by wrought iron
bolts and caps, and in one direction are cast in sets of 2 or 4, which
are afterwards drawn together so as to give more or less heating
surface to the boiler according to the number used.