wires a little stronger, and varying generally from one to two-tenths
of a millimeter in diameter. The current then requires to be a little
intenser. The requisite intensity is easily obtained with elements
of large surface, which have a much feebler internal resistance than
porous-cup elements; and since, for a given number of elements, the
intensity of the current decreases in measure as the internal resistance
of the elements increases, it becomes of interest to diminish such
internal resistance as much as possible. The platinum wires are usually
rolled spirally, with the object in view of concentrating the heat into
a small space, in order to raise the temperature of the wire as much as
possible. There is thus need of a less intense current to produce the
inflammation than with a wire simply stretched out. In fact, the same
wire traversed by a current of constant intensity scarcely reaches a
_red_ heat when it is straight, while it attains a _white_ heat when it
is wound spirally, because, in the latter case, the cooling surface is
less.

[Illustration: FIG. 2--RANQUE'S NEW FORM OF LIGHTER WITH EXTINGUISHER.]

We shall now proceed to the examination of a few practical forms of
electric lighters.

In Fig. 1 will be seen quite a convenient spirit or naphtha lighter,
which has been devised more especially for the use of smokers. By
pushing the lamp toward the wall, the wick is brought into proximity
with the spiral, and the lamp, acting on a button behind it, closes
the current. Pressure on the lamp being removed, the latter moves back
slightly, through the pressure of a small spring which thrusts on the
button. Owing to this latter simple arrangement, the spiral never comes
in contact with the flame, and may thus last for a long time. Mr.