being of course essential that the traffic at the Central Station
should not be interfered with. During these hours, night after night,
trenches were cut at intervals of 10 feet across the roadway
connecting the arrival platforms at the station, and into these were
placed strong balks of timber, across which planks were laid as a
temporary roadway. Beneath these planks, which were taken up and put
down as required, the rock was excavated to a depth of 9 feet, and the
balks supported upon stout props. Then from the driftway or rough
boring beneath well holes were bored to the upper excavation, and
through them the strong upright iron pillars designed to support the
roof of the new tunnel station were passed, bedded and securely fixed
in position. No sooner were they _in situ_ than the most troublesome
part of the task was entered upon, for the balks had then to be
removed in order to allow to be placed in position the girders running
the length of the new station, and resting on the tops of the upright
pillars. From these longitudinal girders cross girders of great
strength were placed, and between these were built brick arches,
packed above with concrete. This formed the roof of the new station.
One portion of it passed under the rails in the station above, and had
to be constructed without stoppage of the traffic. The rails had
consequently to be supported on a temporary steel bridge of ingenious
design, constructed by Mr. C.A. Rowlendson, the resident engineer and
manager of the company, under whose personal supervision, as
representing Sir Douglas Fox, the work has been carried out. With this
device the men were enabled to go on in safety although locomotives
were passing immediately above their heads. After the completion of
the roof the station below was excavated by what is technically called
"plug and feather" work--that is to say, by drilling holes into which
powerful wedges are driven to split the rock.

* * * * *

A STEAM STREET RAILWAY MOTOR.

[Illustration: North Chicago Street Railroad Engine]

While in Paris, President Yerkes, of the North Chicago Street Railway
Company, purchased a noiseless steam motor, the results in
experimenting with which will be watched with great interest. The
accompanying engraving, for which we are indebted to the _Street
Railway Review_, gives a very accurate idea of the general external
appearance. The car is all steel throughout, ex