16, issued April 23, 1901, applied for on July 16, 1897,
he says: "The object of my invention is to produce a method for the
breaking of rock which will be simple and effective, will not require
the hand-sledging or blasting of the rock down to pieces of moderate
size, and will involve the consumption of a small amount of power."

While this quotation refers to the method as "simple," the patent under
consideration covers one of the most bold and daring projects that
Edison has ever evolved. He proposed to eliminate the slow and expensive
method of breaking large boulders manually, and to substitute therefor
momentum and kinetic energy applied through the medium of massive
machinery, which, in a few seconds, would break into small pieces a rock
as big as an ordinary upright cottage piano, and weighing as much as six
tons. Engineers to whom Edison communicated his ideas were unanimous
in declaring the thing an impossibility; it was like driving two
express-trains into each other at full speed to crack a great rock
placed between them; that no practical machinery could be built to
stand the terrific impact and strains. Edison's convictions were
strong, however, and he persisted. The experiments were of heroic size,
physically and financially, but after a struggle of several years and
an expenditure of about $100,000, he realized the correctness and
practicability of his plans in the success of the giant rolls, which
were the outcome of his labors.

The giant rolls consist of a pair of iron cylinders of massive size and
weight, with removable wearing plates having irregular surfaces formed
by projecting knobs. These rolls are mounted side by side in a very
heavy frame (leaving a gap of about fourteen inches between them), and
are so belted up with the source of power that they run in opposite
directions. The giant rolls described by Edison in the above-named
patent as having been built and operated by him had a combined weight of
167,000 pounds, including all moving parts, which of themselves weighed
about seventy tons, each roll being six feet in diameter and five feet
long. A top view of the rolls is shown in the sketch, one roll and one
of its bearings being shown in section.

In Fig. 2 the rolls are illustrated diagrammatically. As a sketch of
this nature, even if given with a definite scale, does not always carry
an adequate idea of relative dimensions to a non-technical reader,
we present in Fig. 3 a perspective il