ix inches wide, and as long as may be needed. At
each end is an enlargement with a hole to receive a pin. In this way any
number of bars can be joined together, and the result of numerous
experiments made at this establishment has shown that under sufficient
strain they will part as often in the body of the bar as at the joint.
The heads upon these bars are made by a process known as die-forging.
The bar is heated to a white heat, and under a die worked by hydraulic
pressure the head is shaped and the hole struck at one operation. This
method of joining by pins is much more reliable than welding. The pins
are made of cold-rolled shafting, and fit to a nicety.

The general view of the machine-shop, which covers more than an acre of
ground, shows the various machines and tools by which iron is planed,
turned, drilled and handled as though it were one of the softest of
materials. Such a machine-shop is one of the wonders of this century.
Most of the operations performed there, and all of the tools with which
they are done, are due entirely to modern invention, many of them within
the last ten years. By means of this application of machines great
accuracy of work is obtained, and each part of an iron bridge can be
exactly duplicated if necessary. This method of construction is entirely
American, the English still building their iron bridges mostly with
hand-labor. In consequence also of this method of working, American iron
bridges, despite the higher price of our iron, can successfully compete
in Canada with bridges of English or Belgian construction. The American
iron bridges are lighter than those of other nations, but their absolute
strength is as great, since the weight which is saved is all dead
weight, and not necessary to the solidity of the structure. The same
difference is displayed here that is seen in our carriages with their
slender wheels, compared with the lumbering, heavy wagons of European
construction.

[Illustration: VIEW OF MACHINE-SHOP.]

Before any practical work upon the construction of a bridge is begun the
data and specifications are made, and a plan of the structure is drawn,
whether it is for a railroad or for ordinary travel, whether for a
double or single track, whether the train is to pass on top or below,
and so on. The calculations and plans are then made for the use of such
dimensions of iron that the strain upon any part of the structure shall
not exceed a certain maximum, usually fixed a