1856.

_Final Report of_ JOHN A. ROEBLING, _Civil Engineer on the Niagara
Railway Suspension-Bridge_, May, 1855.]

[Footnote 2: Lest these statements should sound extravagant, the
reader will please reckon up the amounts for himself. A bank
twenty-five feet wide on top, eight hundred feet long, and two
hundred and thirty feet high, would contain two million cubic yards
of earth; which, at twenty-five cents per yard, would cost half a
million of dollars, exclusive of a culvert to pass the river, of
sixty, eighty, or one hundred feet span and seven hundred feet long.
Twenty trains per day, of thirty cars each, one car holding two yards,
would be twelve hundred yards per day; two million, divided by
twelve hundred, gives 1,666 days.]

[Footnote 3: The most careless observer has doubtless noticed that
the front part of a locomotive rests upon the centre of a track,
having four small wheels; the back and middle part, he will also
remember, is borne upon large spoke wheels,--which are connected
with the machinery; upon the size of these last depend the power and
speed of the engine. The larger the wheels, the less the power, and
the higher the velocity which may be got; again, the wheel remaining
of the same size, by enlarging the dimensions of the cylinders the
power is increased; and the wheels and cylinders remaining the same,
by enlarging the boiler we can make stronger steam and thus increase
the power. There may be seen upon the road from Boston to
Springfield engines with wheels nearly seven feet in diameter, used
for drawing light express-trains; while upon the roads ascending the
Alleghanies may be seen wheels of only three and a half feet diameter,