In 1839, Baldwin invented a geared engine with an independent shaft or axle between the two truck-axles connected by cranks and coupling rods with cranks outside the drivers. This shaft had a central cog wheel engaging on each side with intermediate cog-wheels in turn geared into wheels on each truck-axle, the intermediates having wide teeth, so that the truck could pivot while the main shaft remained parallel with the driving-axle. This type not proving a success commercially, he in 1842 invented for accomplishing the same purpose the six-wheel con nected engine, with the four front drivers combined in a flexible truck, the Lox being rigid in tile frames (usually behind the fire-box) and having inside bearings. The remaining wheels had inside journals run ning in boxes held by two wide and deep wrought-iron beams, one on each side, which were not connected. Their pedestals were bored out cylindrically, and into them were fitted the cylindrical boxes which Bald win patented in 1835. A spherical pin running down from the frame bore in a socket in the beam midway between the two axles. Thus each side beam independently could turn horizontally or vertically under the spher ical pin, and the cylindrical boxes could turn in the pedestals. This was followed by a flexible-beam engine with but four wheels connected to compete with the standard "American " eight-wheel type, with four wheels connected. Baldwin made the forward wheels of smaller diam eter as leaders, but connected them with the front drivers in a flexible beam-truck.
Figure 8 shows the frame of the "American" type of locomotive; Figure 9, of the " Mogul " or ten-wheels' style; and Figure that of the "Consolidation" type. It will be seen how much these differ from the plate construction used in the engines built in other countries.
Arrangement A 111 elial LOC011iOthie 11 1833 the Norris locomotives had the drivers before the fire-box. All the engines built by Baldwin in 183i had the driving-wheels back of the fire-box. The Norris and the Baldwin systems of placing single driving-axles, one behind and the other in front of the fire-box, were aJon. Campbell used two pairs of driving-axles, one pair in front and the other behind. The Forney engine (p/. to2, fig. 2) has both driving-axles between the fire-box and the smoke-box, and the tender and part of the cab are car ried partly by a four-wheeled truck and partly by the main frame of the engine, thus giving the driving-axles a part of the tractive weight with out putting too much upon them. There is no leading truck in the For ney engine proper, but it is frequently built with a " pony" leader. The Hudson "double-ender" (p/. to3, fig. 1) was constructed for the purpose of enabling an engine to run "either way to" for short runs. It has a long wheel-base to give steadiness, yet sufficient flexibility to enable it to round short curves with ease and safety. There are two driving-axles between the furnace and smoke-box and a pony truck at each end. As
this plan still brought the water-tank, with its varying weight, on top of the boiler, a development of this double-ender was a locomotive having at the rear end a four-wheeled truck which carried the tank, and also having a Bissell truck at the front end.
In 1836, Campbell patented the eight-wheeled engine, with four driv ing,-wheels in connection with a four-wheeled truck in front. This, the first engine of the "American " eight-wheeled type, had no equalizing beam (A/. 99, fig. 2). The eight-wheeled connected engine (fig. 7) was intro duced by Baldwin in 1S46, the first one of these having inclined cylinders, as do many engines of the present day built by Porter, particularly those for narrow-gauge service. In 1S46, Norris patented the ten-wheeled engine with six drivers connected. Ten-wheeled outside-connected engines with straight axles were first built by Rogers for the Savanilla Railroad, and the connecting-rod took hold of the outside journal of the main crank-pin.
The "Mogul " engine ( fig 8), having three pairs of driving-wheels coupled together and a two-wheeled truck, was made possible by the invention of the Bissell or " pony " truck, and practicable by A. F. Smith's addition of swing-links. The two-wheeled truck enables the wheels to be placed farther forward than where there are four wheels, and this of course puts a greater proportion of the weight upon the driv ers than is put on the drivers of ten-wheeled engines. A further develop men't of this Mogul type is the "Consolidation" (p.101, f. 8), which has a pony truck and four pairs of driving-wheels coupled together, which system throws a still greater proportion of the weight upon the drivers.
Switching engines are generally built with four coupled wheels and with both axles between the furnace and the smoke-box. These may have separate tenders or have a tank saddled on the top of the boiler. More powerful switching engines are made with six coupled wheels between the fire-box and the smoke-box, and some also have six wheels coupled, but with one of the axles behind the fire-box; but this throws rather too great a proportion of weight upon the front pair. It is best for many reasons to balance the weight of the cylinders and smoke-box by the weight of the fire-box.
The ten-wheel fast-passenger locomotive of the Maine Central Rail road, which is shown in Figure r (p1. 102), is one of ten similar ones in service on that road, and it is claimed that it is a better type of locomotive for fast-passenger traffic than the ordinary American type. This engine has cylinders 19 by 24 inches and drivers 68 inches in diameter; it has a rigid-wheel-base of $6;.. feet and a driving-wheel-base of 12 feet 2 inches. Of the total weight of 118,000 pounds, 94,00o pounds are on the drivers. This engine, in addition to its tender, will pull zoo° net tons at the rate of thirty miles an hour on a level, or 247 net tons on a grade of 15o feet per mile.