Tender-/ocomothrs.—To avoid this difficult connection, which is subject to wear and tear, the tender has been entirely combined with the locomotive—that is, the water-reservoir and coal-bunker have been placed on the locomotive. The term "tender-locomotives" is applied to these constructions, one of which, shown in Figure io, can readily be recognized by the water-boxes placed over the frames. They may, however, be placed in the frames themselves or be arranged on the boiler like a saddle (51. to3, fig. i.) Fairlic's Dufiler heavy trains are moved by two locomotives. If engines with coupled axles and separate tenders are used for the purpose, the tractive power, while it becomes exceedingly large, is very expensive, especially on account of two crews being required. To avoid this disadvantage, Fairlie has inseparably connected two tendered engines, so that they can be handled like one and by one crew. The two boilers of this duplex locomotive consist of a single piece, their fire-boxes being in the centre and the smoke-stacks, with the four cylinders of the two sets of twin engines, being on the outer ends. However, each of these motors is fastened to a truck provided with three axles, to which the term " motor-truck " is applied in contradistinction to trucks (pl. 9S, figs. 8, To), which have only running-axles. The two motor-trucks accom modate themselves to the curves independently of each other, while the long rigid boiler rests on them without preventing their turning, so that it is possible to round sharp curves without danger.
Akver's Duplex to Fairlie's locomotive, Meyer constructed a duplex locomotive, in which the four cylinders were in the centre and the trucks were connected by special rods instead of by the boiler. Both these tender-engines appeared in 1S51 among the competing engines for the Semmering Railway, the system now called Fairlie's being represented by Lausmann's engine "Seraing," and Meyer's by Gfinther's "Wiener Neustadt." A future of great promise was prophesied by many for Meyer's and for Fairlie's systems. As regards the utilization of the entire weight in trac tive adhesion, this prophecy would have been justified, but in many cases, as on the and Brenner railroads, tender-engines are not consid ered suitable, since their adhesion-weight decreases as the water and fuel are consumed, which would make a considerable difference where water and fuel-stations were far apart. Throwing the dead weight of the tender on the driving-axles has for this reason been abandoned on the Semmering Railway, locomotives without trucks, but with four coupled driving-axles and an ordinary tender, being now employed (fig. 4). Moreover, it does not seem advisable to make the tractive power entirely dependent on the adhesion resulting from the weight. Under all circumstances the tires and rails suffer exceedingly from the resulting tangential force, and there are needed considerably higher and more expensive rails and a more solid and costly substructure; so that the comparison made of the contest between the locomotive and the road-vehicle structure, with that between the projectiles and armor-plates, seems very apt. If no axle of the loco
motive were loaded more heavily than any one on the heaviest freight-car, the road and its appurtenances would not need to be so excessively solid as is now required solely on account of the heavy locomotives.
Disturbing consequence of the weights of the pistons, piston-rods, connecting-rods, coupling-rods, etc. being unceasingly thrown backward and forward in rapid alternation, the main and side rods having also a vertical motion, the centre of gravity of the locomotive constantly changes its position, instead of moving, as would be desirable for steady working, only in the direction of propulsion of the entire machine. In consequence also of the varying pressures against the frame, resulting from the use of a crank, the springs carrying the entire structure are constantly subjected to varying stresses, those upon the one side some times being strained more than those upon the other side, and those in front more or less than those behind. From these mechanical causes originate the peculiar short and quick oscillations and swinging, motions, which arc divided into jerking, hammering, and " wee-walling," generally called "disturbing motions." Paktnein,T.—In moving backward and forward the heavy constituent parts by themselves produce motions as if the locomotive were drawn to and fro upon the track (short-and-quick motion), and as if it run waggling in horizontal waving lines (" wee-wahing," reeling). The varying pres sures on the springs impart to the locomotive vertical undulations, swing ing motion (overbalancing or galloping), and rocking as if it were a cradle. The first two of these motions may be in part compensated by balancing weights, which, like the counter-weight for the heavy cranks, are placed on the driving-wheels. The rest may be partially overcome by proper construction. But other circumstances make these compensations unsuit able. It would, therefore, be of advantage to use a construction which contains as few reciprocating masses as possible; or, still better, a con struction with no reciprocating parts and working without a crank.
In this respect, such an engine, for example, as is represented in Figure 9 (pi. with oscillating cylinders in which the pistons move toward and from each other, might solve the problem. Still more suit able, however, would he an engine with rotating piston or follower (a so-called "rotary engine ") fastened directly on the driving-axle, which would use a single cylinder, or at least would not require two in order to overcome the dead points. But on account of the difficulty of sol idly fixing an oscillating engine, and the exceedingly wasteful steam consumption of the rotary engine, the ordinary reciprocating horizontal engine is still retained.