buildings were made in 1854, in a rolling mill at Trenton, N. J., and
were used in the construction of the Cooper Institute, and the building
of Harper & Brothers. For these special rolls, of a special invention,
were made. These have now become obsolete, and a new arrangement is used
for what are known as "structural shapes."

[Illustration: HYDRAULIC SHEARS. THE KNIFE HAS A PRESSURE OF 3,000 TONS,
CLIPPING PIECES OF IRON TWO BY FOUR FEET.]

I have spoken of the use of wood-fuel in the early stages of iron
manufacture in this country, followed by the adoption exclusively of
coal and its products. Then, many years later, came the departure from
this in the use of gas for fuel. The first use of this kind is said to
date as far back as the eighth century, and modifications of the idea
had been put in practice in this country, in which gas was first made
from coal and then used as fuel. Then came "natural gas." This product
has been known for many centuries. It was the "eternal" fuel of the
Persian fire-worshippers, and has been used as fuel in China for ages.
Its earliest use in this country was in 1827, when it was made to light
the village of Fredonia, N. Y. Probably its first use for manufacturing
purposes was by a man named Tompkins, who used it to heat salt-kettles
in the Kenawha valley in 1842. Its next use for manufacturing purposes
was made in a rolling mill in Armstrong county, Penn., in 1874,
forty-seven years after it had been used at Fredonia, and twenty-nine
years after it had been used to boil salt.

Now the use of natural gas as manufacturing fuel is universal, not alone
over the spot where the gas is found, but in localities hundreds of
miles away. It is one of the strangest developments of modern scientific
ingenuity. That enormous battery of boilers, which was one of the most