eservoirs were constructed, capable of holding from one hundred
and fifty thousand to two hundred thousand cubic feet of
compressed air, the average rate of condensation being about two
hundred atmospheres. These reservoirs were properly connected
with the pumping apparatus of the bridge by large cast-iron
mains, so that the supply was continuous, and at an almost
nominal cost. It was by the same power of compressed air that the
tunneling through Mount St. Gothard was effected for the Lyons
and Turin Railway, just completed.

The first operations were to enlarge the shaft so as to form an
opening forty by one hundred feet, English measure. This consumed
the greater part of the year 1849, so that the real work of
sinking was not fairly under way until early in 1850. But from
that period down to the memorable 5th of November, 1872, the
excavation steadily progressed. I neglected to state at the
outset that M. Jean Dusoloy, the state engineer of Belgium, was
appointed General Superintendent, and continued to fill that
important office until he lost his life, on the morning of the
6th of November, the melancholly details of which are hereinafter
fully narrated.

As the deepening progressed the heat of the bottom continued to
increase, but it was soon observed in a different ratio from the
calculations of the experts. After attaining the depth of fifteen
thousand six hundred and fifty feet,--about the height of Mt.
Blanc--which was reached early in 1864, it was noticed, for the
first time, that the laws of temperature and gravitation were
synchronous; that is, that the heat augmented in a ratio
proportioned to the square of the distance from the surface
downward. Hence the increase at great depths bore no relation at
all to the apparently gradual augmentation near the surface. As
early as June, 1868, it became apparent that the sinking, if
carried on at all, would have to be protected by some
atheromatous or adiathermic covering. Professor Tyndall was
applied to, and, at the request of Lord Palmerston, made a vast
number of experiments on non-conducting bodies. As the result of
his labors, he prepared a compound solution about the density of
common white lead, composed of selenite alum and sulphate of
copper, which was laid on three or four thicknesses, first upon
the bodies of the naked miners--for in all dee