ons are easily worked by one man,
who attends to the boiler. The travelling motion is transmitted from the
crane-engines by suitable gear and shafts to the travelling wheels, and
warping-drums or capstans are fitted on a countershaft on the inner side
of each frame, which drums can be driven independently of the travelling
wheels for moving trucks into position below the crane as they are
required for loading and unloading. Smaller cranes may pass with their
loads below the gantry, and a number of these large cranes may be
assembled so as each to work at the different hatchways of a large
screw steamer, or two may be associated together for any exceptionally
heavy lift. The value of elevation of the crane is not only in allowing
the loaded cars to be brought on tracks beneath it, but in giving it
capacity to work over the sides of large vessels, which when light may
rise twenty feet above the level of the quay, and to load or discharge
from trucks on two lines of rails on the land-side of the gantry,
overhead of the trucks on the two lines which run below the gantry.[6]

Blake's stone-breaker, though only represented by model in the United
States section, where it belongs, is shown by two English firms; and
though some Europeans profess to have improved upon its details, no
efficient substitute has been found for it, but it remains the premium
stone-crusher of the world, and has rendered services in the
exploitation of gold quartz and silver ores, and in the crushing of
stones for public works and for concretes, which can hardly be
exaggerated. In testimony taken in the United States in 1872 it was put
in evidence that five hundred and nine machines then in service effected
a direct saving over hand-labor of five million five hundred thousand
dollars per annum.

Steam-pumps are here in force--direct by Tangye and others, and rotary
by both of the Gwynnes, whose name has been so long and is so intimately
associated with this class of machines.

The emery-wheels of Thompson, Sterne & Co. of Glasgow have the same
variety of form and application usual with us, but the firm claims that
while it uses the true corundum emery of Naxos, the American article is
only a refractory iron ore, which soon loses its sharpness and becomes
inefficient. This is a question of efficiency or of veracity which we
leave to the trade. The machine adapted as a tool-grinder has six
emery-wheels for varying characters of work. Four are assorted f