batteries of boilers will provide steam for these engines. Figs. 2, 3,
and 4 show the first section of the installation now in progress; the
four groups of engines (three-cylinder condensing) are shown at 1, 2,
3, and 4; the four groups of boilers ranged behind them at F, F; the
feed water heaters belonging to each group at V V.

[Illustration: COMPRESSED AIR STATION ON THE QUA DE LA GARE, PARIS.
(FIG. 2,3,4)]

The end of the building abuts against the Seine, and the position of
the water conduits for inlet and discharge are indicated at C and A
respectively. The installation, when completed, will include very
extensive arrangements for transporting and storing coal, and the
interior of the boiler houses will be furnished with an overhead
system of rails and carriers for handling the coal automatically, as
far as possible. All the principal mains and steam pipes are made in
duplicate, not only for greater security, but in order that each set
of engines and boilers may be connected interchangeably without delay.
The Seine supplies an ample quantity of water, but not in a condition
either for feeding the boilers, for condensation, or for the air
compressors.

[Illustration: THE NEW COMPRESSED AIR STATION AT PARIS. (FIG. 5, 6)]

Special provisions have therefore to be made to filter the water
efficiently before it is used. For this purpose the water is led to a
group of four filters (see L, Fig. 4); from them it passes into the
tanks, JJ, and is pumped into the heaters. The filters can be rapidly
and automatically cleaned by reversing the flow of water through them.
Figs. 5 and 6 show the general form of the type of engine adopted, as