the oxygen which flows around us, and then
make it pass wherever we please.

The process at present under experiment,
which is not M. Mallet's, is due to M. Tessié
du Motay, and supplies oxygen at so reduced
a price that it can be advantageously employed
in the arts. M. du Motay resolves the problem
by charging with atmospheric oxygen the
substance known to chemists as manganate of
soda, or potash. The oxydation is effected by
directing upon the manganate a current of hot
air, which transforms it into permanganate.
The oxygen which the substance has absorbed
is then driven out by a current of steam heated
to four hundred and fifty degrees. It is the
same legerdemain trick as in the preceding
instance. You borrow oxygen from the air, you
imprison it in a solid substance, and then you
drive it into a reservoir to await your will.
That is the whole secret of the operation. It
is, in short, a simple transfer effected by heat—
a separation of the oxygen from the azote of
the atmosphere, thus giving it to us in a state
of purity. The cost price of oxygen so obtained
by M. du Motay is something less than sevenpence
the cubic yard.

The only novelty, therefore, of the experiments
at the Hôtel-de-Ville lies not, as is
generally supposed, in the mode of lighting, but in
the mode of extracting oxygen from the air.
They have united there, in fact, miniature
gas-works and a system of tubing. The gas-
generator is placed in the cellars of the
Assistance Publique, and the oxygen is thence
conducted in tubes to the four tall candelabra
which light the Place on the side of the Rue
de Rivoli. Six cylindrical cast-iron retorts,
about ten feet in length, are placed one over the
other in a furnace, and made red hot. The first
three are full of manganate of soda, the other
three of permanganate of soda.

A ventilator, worked by a portable steam-
engine, drives a current of hot air into the first.
This air is previously freed of carbonic acid
by passing through a mixture of lime and water.
Here, consequently, the oxygenation is effected.
The apparatus is charged with oxygen extracted
from the air. On the other hand, a boiler
under pressure sends a jet of steam into the
three other retorts full of permanganate, that
is, of oxygenised manganate; and in them, the
disoxygenation takes place. The oxygen stolen
from the air by the first operation is driven off,
and carried away and stored in a gasometer.
By thus successively treating each group of
retorts by the agency of a current of air and
of steam, they are charged with oxygen, which
is then taken from them to be carried by tubes
to its destination.

The act of lighting is thus effected. Each
burner, enclosed in a lamp, is double,
comprising one for the bicarbonated hydrogen and
another for the oxygen, subdividing into two
still narrow conduits, in order to obtain a closer
contact between the gas and a small stick of
compressed magnesia fixed in the middle. The
introduction of the oxygen and the ordinary
gas is regulated by hand, until the magnesia
cylinder gives its maximum of brightness. The
candelabra have each five burners. Of the beauty
of the light there can be but one opinion.

Oxygen light, in fact, possesses great
brilliancy, as well as fixity, even in a high wind,
which is invaluable. During the storm of the
eighteenth of January last, the candelabra
filled with the Drummond light never ceased
to shine, while candelabra holding ordinary
burners were blown out one after the other.
The experiment has also been continued long
enough for M. Tessié du Motay's method of
obtaining oxygen to be held as practically
established; and this is an important fact to note,
even if it were only to be applied to lighting
in special cases. But for lighting purposes
only, it opens a wide horizon; independent of
which, it may possibly effect considerable
modifications in metallurgy.

The superior brilliancy of the new mode of
lighting over the old one is evident. The
flame of common gas looks yellow beside the
Drummond candelabra. But what is required
in order to form a judgment of the real value
of the new system is, to ascertain the actual
cost price of the photometric unity of light. It
is estimated that the oxygen light, according to
the kind of burner employed, may be ten, fifteen,
and even twenty times more powerful than the
light of gas. There would, therefore, be
manifest economy in employing it, if other elements
of appreciation had not to be considered. It
must not be forgotten that lighting by oxygen
requires a double set of pipes and a special
apparatus.

We are also too apt to confound the brightness
of a light with its illuminating power.
Thus, although in the Hôtel-de-Ville experiments,
the magnesia cylinder, brilliant as it
was, did not pain the eye, the reason was that
it was raised five yards above the level of the
ground, whereas, had it been at the usual
height, it would have very disagreeably impressed
the retina. For ordinary uses, it would be
necessary to subdue the glare by the
interposition of an enamelled globe— a gratuitous
waste of light. A glittering point fatigues the
eye and does not sufficiently disperse its luminous
rays. Indeed, the principle of the
dispersion of light for illumination is less generally
considered than it ought to be.

The intensity of a light is of less consequence
than the number of luminous points employed.
In this respect, the new system is clearly
inferior to the one now in operation. Shining
and illuminating are very far from synonymous.
Without coming to any certain conclusion, it
is possible that the Drummond light,
theoretically economical and superior to gas in
intensity, may not present, in actual practice,
the same advantages for general lighting.

M. Henri de Parville— to whom we are
indebted for the substance of this article—therefore
holds that it would be rash to state, as
many have done, that we are on the eve of a
complete revolution in our modes of lighting.