In still rarer cases both a leading and a trailing bogie have been fitted.
Miller, delivered to the South Carolina railroad in 1834, presented a feature which has remained characteristic of American locomotives - the front part was supported on a four-wheeled swivelling bogie-truck, a device, however, which had been applied to Puffing Billy in England when it was rebuilt in 1815.
In any case the details depend upon whether the vehicle concerned is an engine, a wagon or a passenger coach, and upon whether it runs on bogie-trucks or not.
Aspinall on the Lancashire & Yorkshire railway to ascertain the resistance of trains of bogie passenger carriages of different lengths at varying speeds, and the results are recorded in a paper, " Train Resistance," Proc. Inst.
17, four values of L being taken for formula (12) corresponding to trains of 5, 10, 15 and 20 bogie carriages.
Thus 4-4-2 represents a bogie engine with four-coupled wheels and one pair of trailing wheels, the wellknown Atlantic type; 4-2-2 represents a bogie engine with a single pair of driving-wheels and a pair of trailing wheels; 0-4-4 represents an engine with four-coupled wheels and a trailing bogie, and 4-4-o an engine with four-coupled wheels and a leading bogie.
(2) " Four-coupled " type, 4-4-0, with leading bogie truck.
(5) " Four-coupled " type, with a leading bogie truck and a trailing axle, 4-4-2.
It has many advantages for heavy high-speed service, namely, large and well-proportioned boiler, practically unlimited grate area, fire-box of favourable proportions for firing, fairly low centre of gravity, short coupling-rods, and, finally, a combination of the safe and smooth riding qualities of the fourcoupled bogie type, with great steaming capacity and moderate axle loads.
Occasionally a somewhat similar type is designed with the bogie under the fire-box and a single leading axle forward under the smoke-box - an arrangement in favour for suburban tank engines.
(6) " Six-coupled " with bogie, or " Ten-wheel " type, 4-6-0.
Occasionally the American eight-coupled type has a bogie instead of a single leading axle (4-8-0), and is then termed a " Twelve-wheeler," or " Mastodon."
It soon led to an increase in the length of the vehicles; thus in 1885 the Midland railway had four-wheeled bogie third-class carriages, with bodies 43 ft.
Long, holding seventy persons in seven compartments and weighing nearly 18 tons, and sixwheeled bogie composite carriages, 54 ft.
In America the long open double-bogie passenger cars, as originally introduced by Ross Winans on the Baltimore & Ohio railway, are universally in use.
American cars, on the other hand, have long bodies mounted on two swivelling bogie-trucks of four wheels each, and are commonly constructed of steel.
When melted the products separate on the bed (which is made of closely packed sand or other infusible substances), according to their density; the lighter earthy matters forming an upper layer of slag are drawn out by the slag hole K at the flue end into an iron wagon or bogie, while the metal subsides to the bottom of the bed, and at the termination of the operation is run out by the tap hole L into moulds or granulated into water.