MEANS OF COMMUNICATION. 29 
useless ; on the contrary, it is necessary that the other parts of the wheels, the 
nave, spokes, &c., should be annealed, to avoid the constant breakage which 
would otherwise result. It has been attempted to accomplish these two 
ends by casting the tire or tread of the wheel in contact with a ring of 
iron, which chzd/s and very much hardens this part of the wheel, while the 
spokes and nave were cast in sand and permitted to cool gradually, the ring 
or band of iron called the chzld being laid into the mould of sand, so that 
the whole wheel was cast together. The unequal contraction of the iron, 
however, in the rim and spokes in wheels cast in this manner has thus far 
prevented the attainment of a perfectly safe cast-iron wheel. Cast-iron 
wheels have been hooped with a tire of wrought-iron, shrunk on while hot, 
or secured with screws or bolts. The wheels have also been made entirely 
of wrought-iron, by uniting the separate portions of the wheel by welding 
or otherwise ; sometimes the tire has been made of steel, at others the body 
of the wheel has been made of wood suitably combined with iron; indeed 
countless combinations of wood, steel, wrought and cast iron have-been 
tried in the effort to obtain a cheap, durable, and safe wheel. PU. 5, fig. 18, 
is a portion of a wrought-iron wheel and axle; dcis the axle, a a spoke 
welded to the nave, which is made in one piece with the axle. These wheels 
are safe but expensive, and are much used upon passenger cars in England. 
In America cast-iron is very generally used; it is more durable upon the 
tread, but more liable to break than wrought-iron. /7%g. 14 is a section 
through a wheel in which wooden spokes 0 are introduced between the rim ¢ 
and nave a, a plan not now much used. The diameter of car-wheels is 
usually three feet, with a thickness upon the tread of three or four inches. 
Railroad axles are of wrought-iron, and require to be carefully proved 
before being put in use, as a small flaw may cause a breakage, and conse- 
quently loss of life and property. 
The bearings or gudgeons are turned cylindrical and run in composition 
boxes, which must be capable of carrying a supply of oil for lubricating 
the bearing parts and preventing undue friction. When this has not been 
attended to with care, the heat has become so excessive as to melt the brass 
bearings above the journals. 
Pl. 5, jig. 15, represents a journal-box of approved construction in longi- 
tudinal section. Here the oil is placed in a vessel in the top of the box, 
and is permitted to drop slowly upon the axles through the hole / in the 
bearing, from the end of a wick, the other end of which is in the oil-box 
above. The oil that drips from the journal is drawn off from the bottom 
of the box and may be used a second time. 1.5, jig. 16, shows a method 
of keeping the journal always lubricated without the use of the wick and 
without waste of oil; the ring gis turned upon the journal and descends 
into the box below the level of the surface of the oil, which is poured in at 
the opening 2. 
The bodies of the cars are variously constructed according to the use to 
which they are to be put, whether they be for the transportation of passen- 
gers, freight, or animals. The passenger-cars are differently constructed upon 
almost every railroad. In Europe there are three or four classes of cars, and 
ICONOGRAPHIC ENCYCLOPZDIA.—VOL. IV. 39 609 
