lectures, in amphitheatres and drawing-rooms, a
brilliant experiment has been running the round,
astonishing the curious beholder. A savant,
sometimes in a white cravat, sometimes in a
black one, drawing from his pocket a white
thread of metallic aspect most carefully wrapped
in paper, promises to illuminate the room for
several seconds with all the splendour of electric
light, by simply burning his bit of wire.

A candle is brought; the extremity of the
magnesium wire is thrust into the flame, and
instantly a dazzling brightness radiates in all
directions. The wire emits, in the shape of
flame, an extremely tenuous vapour, which
burns with unexampled violence. It is
completely encircled by a bright halo which
terminates, upwards, in white smoke, and downwards
in a drooping residuum entirely composed of
magnesia. The Abbé Moigno, well known in
scientific literature, appears to have been the first
to exhibit in France this remarkable property of
magnesium, which he did last summer at one of
the meetings of the Association Scientifique,
before M. Duruy, the present Minister of Public
Instruction.

Magnesium is obtained by reducing the
anhydrous chloride of that metal with sodium.
As what follows is entirely derived from French
sources, I give the details in metrical weights
and measures. The reader, although unused to
them, will readily understand them, by
remembering that a kilogramme, more than two pounds
avoirdupois, is made up of a thousand grammes;
and that a metre, more than an English yard, is
subdivided into a hundred centimetres and a
thousand millimetres. M. Gaudin, calculator
at the Bureau des Longitudes, who has carefully
studied questions connected with lighting,
has recently published an excellent treatise on
the cost of lighting by magnesium, with reference
to its immediate application. I avail
myself of his conclusions, as quoted by M. Henri
de Parville, in his able feuilleton in the
Constitutionel.

Magnesium is not much heavier than wood.
It is silvery white, very volatile, melts at a
cherry-red heat, has little tenacity, but is ductile
enough to be drawn into wire the third of a
millimetre in diameter. Magnesium,
unfortunately, is very dear—forty-eight pounds the
kilogramme. Any serious thoughts of lighting
Paris by means of strips of this metal, are, therefore,
quite out of the question. Nevertheless,
certain employments which seem ready made
for its application, merit careful examination.
Whenever, in fact, it is required to concentrate
on one point, for a short space of time, a great
illuminating power, it is certain that magnesium
may be employed with great advantage.

Photographers, for instance, instead of having
recourse to the electric light—which is difficult
to instal in its place, and complex in its management
—might substitute for it magnesian light.
With this object, trials have been made which
are expected to result in complete success. In
surgery, for the examination of sinuses, nothing
will be simpler or more convenient than to make
use of the new light. The navy also may
profitably employ it for signals. At twelve miles'
distance by day, at thrice that distance by night,
it will be easy to hold communication.

According to M. Gaudin's estimate, the
examination of a diseased sinus would cost one
halfpenny; the taking of a portrait, by means
of a light of five hundred bougie power during
twenty seconds, would cost fivepence. A signal
at sea with one hundred bougie power, one
penny. The illumination of a trench with the
light of a thousand bougies, affording a clear
inspection of a length of a thousand, and a
breadth of five-and-twenty metres, would cost
from ten to twenty pence—considerably less
than the price of firing a cannon. Finally, a
telegraphic signal consisting of four or five
eclipses or changes of colour, with a
hundred bougie light, would only cost one single
penny.

M. Gaudin based his calculations on the
photometric results obtained by M. Bunsen.
A wire of magnesium, the third of a millimetre
in diameter, has, in round numbers, the same
illuminating power as seventy bougies or wax
candles. And it takes a minute to consume a
wire one metre in length and the tenth of a
gramme in weight. According to this, at the
present price of elevenpence-halfpenny per
gramme, that quantity of magnesium would
afford, during one minute, a light equal to that
of seven hundred bougies, or to that of seventy
lamps of ten-bougie power each, which lamps, if
fed with ordinary oil, cost one penny per hour.
Multiplying elevenpence-halfpenny by sixty,
you have the price per hour of magnesian light,
or about tenpence for each ten-bougie power;
which is ten times dearer than lighting by oil.
These few figures suffice to show that, under
present circumstances, magnesian light can be
advantageously employed only in particular
cases.

It ought to be added, that when its employment
becomes more extensive, it is more than
probable that—as almost always happens in
similar instances—its cost price, now very high,
will notably diminish. The elements of its
production, in fact, are not costly. Its price,
in M. Gaudin's opinion, might be expected to
fall as low as forty shillings the kilogramme.
From that time, by rendering it more ductile
through the admixture of foreign substances, it
might be drawn into wire as fine as a hair; and
under those new conditions would be applicable
to domestic lighting at the same price as that of
oil.

What a convenient invention! What a
luxurious light! No more greasy liquids to
handle; no more snipping and snuffing of wicks;
no more cleanings, and scrubbings, and polishings;
no more oil-cans to fill and to fetch! It
really is not unreasonable to hope that the
experimental display, which is now the fashion,
will be productive of useful results, and assume
the phase of an industrial application. To be
moderate in our expectations, we may give up
the idea of employing it for the lighting of