he plate, the better it is able to absorb the
energy of impact without injury to itself.

4. That the backing must be as rigid as possible.

* * * * *

[FROM ENGINEERING.]

THE COMPRESSED AIR SYSTEM OF PARIS.

The demand for compressed air as a motive power is constantly
increasing in Paris; the company, according to its official reports,
is financially prosperous, and it seems difficult to understand how it
should continue as an actively going concern, unless it at all events
paid its way. The central station of St. Fargeau, originally started
on modest lines, for maintaining a uniform time by pneumatic pressure
throughout Paris, has grown rapidly to very large proportions, though
it has never been able to supply the demand made on it for power; and
at the present time a second and still larger station is being
constructed in another part of Paris. We confess that we do not
understand why such large sums of money should continue to be spent if
the enterprise is not commercially a sound one, nor how men of such
eminence in the scientific world as Professor Riedler should, without
hesitation, risk their reputation on the correctness of the system, if
it were the idle dream of an enthusiast, as many persons--chiefly
those interested in electric transmission--have declared it to be.

[Illustration: Fig. 1.--MAP OF PARIS WITH ST. FARGEAU STATION]

In describing the developments that have taken place during the last
two years, we shall confine ourselves entirely to the details of a
report recently made on the subject by Professor Riedler. As soon as
it became evident that a very largely increased installation was
necessary, it was determined that the new central station should be as
free as possible from the defects of the first one. These defects,
which were the natural results of the somewhat hasty development of an
experimental system, were of several kinds. In the first place, so
large a growth had not been contemplated, and the extensions were
made more or less piecemeal, instead of being on a regular plan; the
location of the central station itself was very unfavorable, both as
regards the facilities for obtaining coal and other supplies; the cost
of water was excessive, and the amount available, inadequate.

This evil was partly remedied by elaborate arrangements for cooling
the injection water so that it could be repeatedly used, a device
costly and ineffective, and res