MAGAZINE OF SCIENCE AND ART. 03 
triple of diminishing the amount of useless weight 
carried in a train. This principle is, that the body of 
a car or waggon is carried by two four-wheeled trucks, 
one at each end. The hodv is attached to these trucks 
by means of a pintle in the centre, the weight resting 
on small rollors at each side. The main framing of 
the truck is supported on springs resting on tho axles, 
and the pintle and rollers are fixed to a cross-beam, 
which is attached by springs to the main framing ; so 
that between the body of the car and the axles are a 
double set of springs. India-rubber springs are in 
general use, but they often become bard; consequently 
sometimes steel springs are used, with great advantage* 
Any side movement which might result from the slight 
play allowed to the cross-beam is counteracted by springs 
placed between its ends and the framing. An iron 
hoop attached to the framing passes under the axle on 
each side so as to support the axle in case it should 
break. 
The bearings do not differ materially from those used 
in England. But the axle-box is formed so as to allow 
of oil being used as a lubricator, as it is well adapted to 
withstand heat and cold. The oil is contained in the 
lower part of the axle-box, cotton waste being pressed 
in to prevent it from shaking about, as well as to keep 
it in contact with the axle ; the front is screwed on, 
and, at the hack, a leather fits close round the axle, and 
jrevents the admission of dust. It is stated, that under 
avourable circumstances, this kind of box will run 
sometimes for a month -without requiring to be touched, 
but there is great difficulty in obtaining good oil. 
The wheels used on American railways are of cast- 
iron, with chilled tyres. The wheels are from 30 to 36 
inches in diameter, made without spokes. These wheels, 
when made by the best makers, will run from 60,000 
to 80,000 miles before the tyres are worn, and they are 
said not to bo liable to break ; they weigh rather more 
than 500 lb., and cost from £3 to £3 10s. each; they are 
not of course so true as turned wheels, but their first 
cost is less; they wear well, and during the time they 
last they require no expenditure for turning up ; any 
crack can bo more easily detected by sounding w ith a 
hammer, and when a wheel breaks it does not always 
do the mischief that is done bv a broken tvre. Chilled 
cast-iron tyres are used on some of the railways for the 
driving-wheels of engines; they are made 3 to 3£ inches 
thick, and G inches broad, and cylindrical; they are 
bored out to a true cone to fit the centre, which is’ also 
of cast-iron, turned to a similar cone, and secured in 
place by screws. These chilled castings are stated to 
be preferable to steel, or to wrought iron, on account of 
their being less liable to fracture in frost. The iron of 
which they are made is of a very superior quality, aud 
great practical skill is necessary in the operation. ^ It 
is stated that there are only three firms in the United 
States whose wheels are fully to be relied upon. 
No force is necessary in coupling the care, as the ends 
of the draw-bar or bumpers, abut against each other; 
a shackle is introduced through the opening behind, and 
two pins are passed through the eyes; about an inch 
play being all that is allowed. An iron shackle is 
generally used; hot on some railways the shackle is 
made of oak 18 inches long, 2 inches thick, 6 inches 
broad, -with holes for the pins inch 2 inch, at a 
central distance apart of 12 inches The block, as well 
as each hole, is hound with iron; hut the iron band 
round the block is divided on each side at tho centre, so 
that if a car leave tho rails the side wrench would break 
the shackle transversely. 
In coupling passenger cars the man stands on the 
platform at the end of the car; hut in freight cars, 
when there is no platform, the following self-acting con¬ 
trivance for dropping in the pin, is sometimes adopted 
to prevent injury to the man employed. When two cars 
are to be coupled, the pin in the bumper of one of tho 
cars is supported by means of a ball, and the shackle is 
fixed by its pin in the bumper of- the other car; when 
the cars are moved one against the other, the shackle in 
one bumper pushes back the - ball in the other, and al¬ 
lows the pin to drop into the hole. 
All I passenger cars, and almost all freight cars, are 
supplied with breaks, which are applied to all the 
wheels, worked from either end of tho car. The blocks 
of the breaks are lined with plates of cast-iron; and it 
is never intended that the wheels should be completely 
skidded. 
On the Philadelphia and Reading Railway there is 
an arrangement by which a sudden check in the speed 
of the engine applies breaks to the wheels of all the 
cars. 
Passenger and emigrant cars, covered freight cars, or 
low-sided and platform cars for timber and minerals, 
&c., are placed upon the trucks I have described. Upon 
some railways coal and ballast waggons are used, con¬ 
structed in the same manner as those upon English 
rail wavs. 
The bodies of the passenger cars aro from 30 to 45, 
and even GO, feet in lengthf This length render it ne¬ 
cessary that the sides should be supported by a truss, 
either in the framing or by iron trussing-rods below. 
On lines of 4 ft. 8£ in. guage the care are about 9 feet, 
and on the New York and Erie, 10 feet wide, aud from 
(j ft. to 7 ft. 6 in. high. There are two classes of pas¬ 
senger care, of which one is limited to the conveyance 
of emigrants, Tn the centre of each end of the cars is 
a door, conducting to a small platform, about 2 ft G in. 
wide, from which steps descend on either side to the 
ground. There is a railing to the platform, with an 
opening to allow passengers to pass from the platform 
of one car to that of another, and thus through the 
whole train. On many railways this free passage is 
not allowed to passengers, hut the foremost door of each 
car is locked, so that all passengers must enter at the 
rear door, and the conductor or servants of the train 
alone pass through with keys. 
(To be continued) 
CORRESPONDENCE. 
THE MARBLE AND LIMESTONE QUARRIES 
OF NEW SOUTH WALES. 
To the Editor of the Sydney Magazine of Science 
and Art . 
Sir,—In the second number of your Magazine, for 
the 15th of J illy ultimo, you have invited attention to 
the scarcity and expense of Lime in Sydney ; and the 
too general use of the produce of calcinated shells. 
As this is a subject which was, some rears ago, one of 
immediate importance to myself, I will request you to 
allow space in your columns for a few remarks in" refer¬ 
ence to your paper. 
You do not seem to be aware that, throughout the 
discovered parts of New South Wales, there nave been 
found extensive quarries of marble and limestone; equal 
in the quality of their yields to any that have yet been 
worked in other parts of the world. At this I am not 
surprised, seeingjfiat, in Sydney, the use of stone-lime, 
for building purposes, has been, since the year 1842, of 
a very limited character; and even at that date its in¬ 
troduction lasted but a brief time. A few words will 
explain this abandonment of its use. 
Upwards of a quarter of a century ago; the existence 
of valuable marble and limestone quarries in the inland 
counties of Argvle, Bathurst, and Murray was well 
known, both to the local government and the «ettlers in 
those locales; but whilst in building the houses of 
Goulburn aud Bathurst, mortar and plaster, composed 
of tho linae yields of these quarries, were exclusively 
used, their great distance from Sydney, and the prohi¬ 
bitory prices of laud carriage, precluded the idea of 
bringing this valuable commodity down to the metro¬ 
polis. 
In 1834, however, my lamented friend, the late Colonel 
Sir Thomas L. Mitchell, announced tho discovery of 
valuable marbles of various colours at Piper’s Creelc, a 
short distance from its confluence with the Maria River, 
about two days sail from Sydney. With the exception 
