cup is inserted an iron tube D extending nearly to the top. This tube projects from the bottom of the cup, where it is tapped for the purpose of fixing the cup on the part of the engine which it is intended to lubricate. The hole into which the cup is screwed communicates with the rubbing surface, and some cotton thread is passed through the tube dipping into the oil in the cup at the one end and touching the moving part at the other. This thread acts as a siphon, and constantly drops oil on the rubbing surface.

The tender is a carriage attached behind the engine and close to it, carrying coke for the supply of the furnace, and water for the boiler. The coke is contained in the space R", (fig.98.100.) surrounded by a tank r' containing water to feed the boiler. The feed for the boiler is conducted from the tank through a pipe descending downwards and in a curved direction, p” q”, fig. 98., and connected with a horizontal pipe K, fig. 97. A cock is provided at p", by which the supply of water to this pipe may be cut off at pleasure. Another cock is provided at t', fig. 97., where the curved pipe joins the horizontal pipe by which the quantity of water supplied to K may be regulated by opening the cock more or less fully. The handle of this cock rises through the floor of the engine, so that the engineer may regulate it at discretion. The pipe K being conducted under the engine, as represented in fig. 97., terminates in a vertical pipe, of greater diameter, containing two valves, both of which open upwards, and between these valves to this vertical pipe is attached a force-pump, by which the water is drawn from the horizontal pipe K into the vertical pipe к', and from the latter is driven into a delivery-pipe by which it is forced into the boiler. The details of the interior of this feed-pump are represented on a larger scale in fig. 111. The extremity of the horizontal pipe K' is represented in section at H, where it is joined on by a screw to the bottom of the vertical pipe which is represented in fig. 97. at K, and which is here represented in section. The vertical pipe, represented in fig. 97. consists of several parts screwed together by nuts and bolts passing through flanges. The lowest piece I is attached by a flange to the piece L: within these is contained

which forms the valve shall rest in water-tight contact with it. The ball is turned and ground to an accurate sphere, and whatever position it assumes upon its seat its contact will be

perfect. It is guided in its upward and downward motion by several vertical bars which confine it, and which are united at the top, so as to limit the upward motion of the ball. A screw v' is inserted in the bottom of the piece 1, by removing which access can be obtained to the valve. The piece L is secured to the short pipe & by nuts and bolts passed through a flange. The pipe & is cast upon the end of the feed-pump a. On the foremost end of this feed-pump is constructed a stuffingbox c of the usual form, having a gland D forced against packing by nuts and screws E. The plunger B is turned so as to be truly cylindrical, and moves in water-tight contact through the gland D. The plunger not being in contact with the inner surface of the pump-barrel a, the latter need not be ground. The horizontal rod by which the plunger B is driven is attached at its foremost extremity to an arm which projects from the rod of the steam-piston, and consequently this plunger is moved through a space equal to the stroke of the steam-piston. In this case that space is eighteen inches. The

upper end of the vertical tube G is attached by screws and a flange to a piece P containing a valve R similar in all respects to the lower valve Q, and like it opening upwards. A screw v is introduced at the top by which access may be obtained to this valve. This screw also presses on the crown of the guides of the valve, so as to hold it down by regulated pressure. At the side of this upper piece P is inserted a horizontal tube M connected with the end of the delivery-pipe N. This latter is continued to the boiler with which it communicates at the fire-box. When the plunger в is drawn out of the pump-barrel A, the spherical valve a being relieved from its downward pressure is raised, and water passes from the pipe H through the valve o into the vertical pipe G; the lower valve Q then closes and stops the return of the water. The plunger в returning into the pump-barrel a then forces the water against the upper valve R and drives it through the delivery-tube N, from which its return is prevented by the valve R. When the delivery-tube N is filled with water throughout its whole length, every stroke of the plunger will evidently drive into the boiler a volume of water equal to the magnitude of a part of the plunger eighteen inches in length.

Until within the last few years, locomotive engines were supported on only four wheels; they are, however, now almost universally supported on six, the driving wheels being in the middle. To give greater security to the position of the engine between the rails it is usual to construct flanges on the tires of all the six wheels. Mr. Stephenson, however, has been in the practice of constructing the driving wheels without flanges, and with tires truly cylindrical, depending on the flanges of the two pairs of smaller wheels to maintain the engine between the rails. The wheels of the engine here described are constructed in this manner. The driving wheels D' are fixed on the cranked axle c', and are five feet in diameter. The other wheels L' M', the one being placed immediately behind the smoke-box, and the other immediately behind the fire-box, are each three feet six inches in diameter,

side of each rail keeps the engine between the rails. Each pair of these small wheels, like the driving-wheels, is fixed upon their axle. The axles are 3 inches diameter, and project beyond the wheels, the projecting part supporting the frame of the engine and turning in brasses. Upon these brasses rest springs, which bear the whole weight of the engine. These springs having nothing between them and the road but the wheels and axles intercept and equalise the sudden shocks produced by the rapid motion upon the road.

When an engine is required for the transport of very heavy loads, such as those of merchandise, the adhesion of one pair of working wheels is found to be insufficient, and, in such cases, one of the two pairs of wheels L'M' is made of the same diameter as the wheels which are placed upon the working axle, and a bar is attached to points on the outside of the wheels at equal distances from their centre, connecting them in such a manner that any force applied to make one pair of wheels revolve must necessarily impart the same motion to the other pair. By such means the force of the steam is made to drive both pairs of wheels, and consequently a proportionally increased adhesion is obtained.

The velocity which an engine is capable of imparting to the load which it draws depends upon the rate at which the pistons are capable of being moved in the cylinders. By every motion of each piston backwards and forwards one revolution of the driving wheels is produced, and by each revolution of the driving wheels, supposing them not to slip upon the rails, the load is driven through a distance upon the road equal to their circumference. As the two cylinders work together, it follows, that a quantity of steam sufficient to fill four cylinders supplied by the boiler to the engine will move the train through a distance equal to the circumference of the driving wheels; and in accomplishing this, each piston must move twice from end to end of the cylinder; each cylinder must be twice filled with steam from the boiler; and that steam must be twice discharged from the cylinder through the blast-pipe into the chimney.