s deprived of its carbonic acid; the diver
also carries a supply of compressed oxygen from which to add to the
remaining nitrogen oxygen, in substitution for that which has been
burnt up in the process of respiration. Armed with this apparatus,
a diver is enabled to follow his vocation without any air-tube
connecting with the surface, indeed without any connections whatever.
A notable instance of a most courageous use of this apparatus was
afforded by a diver named Lambert, who, during one of the inundations
which occurred in the construction of the Severn tunnel, descended
into the heading, and proceeding along it for some 330 yards (with the
water standing some 35 feet above him), closed a sluice door, through
which the water was entering the excavations, and thus enabled the
pumps to unwater the tunnel. Altogether, on this occasion, this man
was under the water, and without any communication with those above,
for one hour and twenty-five minutes. The apparatus has also proved to
be of great utility in cases of explosion in collieries, enabling
the wearer to safely penetrate the workings, even when they have been
filled with the fatal choke-damp, to rescue the injured or to remove
the dead.

CONSTRUCTION OF TUNNELS.

With respect to the subject of tunneling thus incidentally introduced,
in subaqueous work of this kind, I have already alluded to that which
is done by "cut and cover," but where the influx of water is a source
of great difficulty, as it was in the old Thames tunnel (though in
this case for water one should read silt or mud), I do not know that
anything has been devised so ingenious as the Thames tunnel shield;
improvement has, however, been made by the application of compressed
air.

In the instance of the Hudson River tunnel, the work was done in the
manner proposed so long ago as the year 1830 by Lord Cochrane (Earl
Dundonald) in that specification of his, No. 6,018, wherein he
discloses, not merely the crude idea, but the very details needed for
compressed air cylinder-sinking and tunneling, included air-locks
and hydraulically-sealed modes for the introduction and extraction of
materials. I may, perhaps, be permitted to mention that some few years
ago I devised for a tunnel through the water-bearing chalk a mode of
excavation by the use of compressed air to hold back the water, and
combined with the employment of a tunneling machine. This work, I
regret to say, was not carried out. But there ar